Dalton’s Chemical Atoms vs. Duhem’s Chemical Equivalents

Abstract. In response to Paul Needham, I defend Dalton’s chemical atomism as

explanatory of the phenomena of concern to chemists of the early nineteenth century.

I then examine Duhem’s contrasting anti-atomistic account of chemistry from the late

nineteenth century. I show that the difference between Dalton and Duhem goes much

deeper than their positions on atomism; it is a fundamental difference in their views

on the place of explanation in science. I conclude with a few brief comments on the

separability of a theory’s explanatory status and its acceptance.

Word Counts: Abstract: 88 Article (including footnotes, captions, and references): 4863 words Author Contact Information Karen R. Zwier Department of History and Philosophy of Science University of Pittsburgh 1017 Cathedral of Learning Pittsburgh, PA 15260 krzwier@gmail.com

Acknowledgements

I thank Thomas Cunningham and Julia Bursten for helpful comments on this paper. I

also thank Alan Chalmers for an interesting seminar on the history of atomism in the

fall of 2007, which spurred my work on this topic.

1. Introduction. John Dalton’s chemical atomism has come under recent criticism in several

provocative articles by Paul Needham (2004a, 2004b, 2008). One of Needham’s theses is

that Dalton’s atoms “gave us no explanation at all” (2004b, 1039). He refers to Dalton’s

theory of atoms as “unilluminating”; he claims that atoms could not explain the difference

between compounds and solutions, were unhelpful as an explanation of constant and multiple

proportions, and could not explain chemical affinities. Needham’s position is an outgrowth

of his emphasis on a thermochemical definition of substance and his anti-microstructuralist

view (see Needham 2000), but his criticisms are also largely inspired by the anti-atomistic

arguments of Pierre Duhem. Needham claims that Duhem “clearly thought that Daltonian

atomism provided no explanation of the laws that it entailed” (2008, 925).

I argue a contrary view in this paper, in three parts:

1. Contrary to Needham’s main claim, I aim to show that when Dalton’s atomism is

examined in its own context and relative to the questions that Dalton himself was

posing, it is indeed an explanatory theory;

2. And contrary to his subsidiary claim about Duhem, I aim to show that even Duhem

admits that Daltonian atomism is explanatory of some very basic and fundamental

facts about chemistry. I will discuss his reasons for rejecting atomism despite this

admission.

In support of the above points, this paper will examine the views of both Dalton and Duhem

on explanation and its role in science, as well as their opposing attitudes toward chemical

atomism.1 In Section 2, I will make some observations about Dalton’s attitude toward

explanation and how he might have understood its role in science. I will then defend

Dalton’s chemical atomism as explanatory of the laws of constant and multiple proportions,

the distinction between compounds and solutions, the law of partial pressures, and the

homogenous constitution of mixed gases. In Section 3, I will turn to Duhem and examine his

view of explanation and its non-role in science. I will then give an overview of his argument

that all of chemistry at his time could be done without reference to atoms and without any

atomic explanations. In this argument, he appears to take the surprising position that

chemical atomism was explanatory of many basic phenomena in chemistry, but not

explanatory enough for to qualify for acceptance. After examining these two cases, I will

close with a few tentative conclusions about the relationship between acceptance of a

scientific theory and that theory’s explanatory value.

2. Dalton’s chemical atoms. As far as is possible to tell at a distance of two centuries,

Dalton seemed to be relatively happy with his theory and its explanatory power; he defended

it until his death. For Dalton, his role as chemist and philosopher of chemistry was one and

1 Due to limitations of space, I will not attempt in this paper to define or use a particular

account of explanation. I will merely attempt to characterize Dalton’s and Duhem’s own

views on explanation, and address the relationship of these views to their respective

acceptance and rejection of atomism.

the same. He valued explanation above all else; his manuscripts and his published papers are

full of speculative theories and assessments of how well the various possibilities that he had

imagined could explain established facts.2 Furthermore, Dalton seemed to seek out problems

in which there existed no explanation for a phenomenon. Examples of Dalton’s penchant for

explaining the unexplained include his work on color blindness, the aurora borealis, and the

constitution of the atmosphere (just to name a few).

Explanation was the goal of Dalton’s scientific work. The discovery of laws and

regularities was never enough for him; he sought out causal-mechanical accounts that gave

rise to the laws. For example, although we attribute to Dalton the discovery of the law of

partial pressures, he saw this not so much as a discovery but as an empirical fact of note; his

real achievement in his own eyes was his theory about what was going on under the surface

to create the effect (see Dalton 1801, 1802). The same can be said of much of the rest of his

scientific work. In this section, I will attempt to elucidate the chemical phenomena that

Dalton took himself to be explaining with his chemical atomism and defend his atomism as

explanatory.

2 For example, in an early article, Dalton chooses to reject or accept various hypotheses on

the ability of each to explain certain facts (1801, 243). In another article from the same

period, he states that his goal is explanation (1802, 538-39). For one of Dalton’s more

extended discussions of his search for explanations, see his manuscript for an 1810 lecture

reproduced by Roscoe and Harden (1896, 13-18).

2.1. Constant and multiple proportions. One of the first and most basic chemical

facts that Dalton took himself to be explaining was the law of constant proportions—i.e. the

fact that chemical compounds are made up of constant proportions of elements by weight.

Dalton reasoned that there must be ultimate particles of elements whose weights form the

basis of these proportions. Needham criticizes this explanation in the following way:

Clearly, the homogeneity of compounds means that smaller quantities contain smaller

amounts of the elements, although in the same proportion as the larger quantity. But

it is hardly explanatory to say that quantities of hydrogen and oxygen combine in

fixed proportions by weight to form water because hydrogen and oxygen comprise

smaller chunks which combine in fixed proportions by weight to form water. This

merely repeats what has to be explained on a smaller scale. Not only that; it seems

that it must be ultimately repeated on an invisible scale, as though taking the ultimate

combining units out of sight provides the magic explanatory ingredient. (2004b,

1041)

In my view (and presumably Dalton’s), taking the ultimate combining units out of sight is

precisely the “magic” explanatory ingredient. Fixed proportions of chemically indivisible

particles on the invisible level explain homogeneity on the level of our senses. We have no

direct evidence that there is homogeneity “all the way down”, because we cannot see “all the

way down”. Therefore, Dalton did not need to provide an explanation for anything but

homogeneity on the sensible level. On the contrary, after the discovery of constant

proportions, anyone who rejected atomism and proposed that it is possible to have

homogeneity “all the way down” had to provide a reason for chemical combination only

occurring in specific proportions. Otherwise there is no explanation for the fact that the

elements in chemical combinations always occur in specific weight ratios. Why should there

not be a continuum of combinatory ratios?

On the basis of chemical atomism, Dalton saw that there was also a straightforward

explanation of the law of multiple proportions. Elements combine in simple, integer

multiples of their characteristic weights because there are integral bits of these same elements

that remain undivided in chemical reactions. Configurations that are chemically stable (i.e.

chemical compounds) will always manifest integral proportions because of the integral bits

that remain intact underneath the chemical change. His atomism also explained what

happens in chemical reactions: there are least parts of chemical elements which remain

undivided in such reactions, but which separate from each other and recombine in a new

arrangement (see Dalton 1808, 212). Dalton’s explanation helps us to understand why it

should be possible to break down a chemical compound and later build it back up again:

there are least parts of each element that remain intact throughout the entire process.

It is essential to note that the basic notion of atomism for which I defend Dalton is

chemical atomism.3 It is not a physical atomism of in-principle indivisible particles.4 The

3 It is debatable whether or not Dalton himself espoused physical atomism or not. It seems

that Dalton was agnostic about the divisibility of his atoms, but it is uncertain whether this

former hypothesis is sufficient by itself to explain the law of definite proportions and the law

of multiple proportions. Chemical atomism is the hypothesis that each element has a

minimum particle such that, if divided further, would cease to be that element. The

hypothesis entails that if a chemical compound known to be made up of two or more

elements is subjected to division after division, the process will necessarily reach a point at

which the chemical compound will no longer be that chemical compound when divided

further, but will be separated into its individual elements. During chemical transformations,

compounds are divided into their constituent particles, the elemental particles themselves, but

no further.

2.2. Chemical compounds vs. solutions. The background for another of Needham’s

criticisms of Dalton’s atoms comes from Joseph Proust’s work in the early nineteenth

century, which established a distinction between compounds and solutions. Both compounds

and solutions were considered “homogeneous mixtures”. Proust showed that, independent of

temperature, pressure, and the process by which they are synthesized, compounds are made

agnosticism came from an uncertainty about which elements are true elements, or an

uncertainty about whether the atoms of elements could be broken down further. For relevant

texts, see Dalton (1808, 212, 216, 220) and Roscoe and Harden (1896, 111).

4 Rocke (1984, 12-13) defends the historical and philosophical value of the distinction

between physical and chemical atomism.

up of constant proportions of elements. Solutions, in contrast, contained varying proportions

of elements. In light of Proust’s result, Needham proposes that any explanation of the law of

constant proportions in compounds must also be an explanation of the difference between

compounds and solutions. He claims that Dalton’s atoms did not provide such an

explanation (2004b, 1040-41).

But Dalton did make a distinction that is directly relevant to the difference between

compounds and solutions. His distinction was between a pure elastic fluid and a mixed

elastic fluid. A pure elastic fluid is “one, the constituent particles of which are all alike, or in

no way distinguishable” (Dalton 1808, 145). These identical constituent particles could be

either simple atoms or compound atoms (Dalton’s term for “molecule”). A mixed elastic

fluid, on the other hand, is one in which the particles of two or more pure elastic fluids

mechanically diffuse through one another in the same space, but do not unite chemically

(1808, 150). If the mixture contains anything other than certain specific proportions of

elements required to assemble the new types of particles, it will remain a mere mechanical

mixture.5 If, however, two or more elastic fluids are mixed and the various types of particles

are present in certain specific proportions, the different types of particles will unite—i.e.

5 Dalton felt that his theory was especially powerful in explaining the fact that differing

amounts of water vapor could be absorbed by different gases under the same circumstances,

and by the same gas under different pressures; he held that this was a case of mixture, not

chemical combination (1808, 151-153).

chemically combine—such that they form new compound particles (1808, 169). What was

originally a mixed elastic fluid will have become a pure elastic fluid, because its constituent

particles are now all alike.

Using his theory of the constitution of mixed gases, Dalton also attempted an

explanation of the law of partial pressures (i.e. the additivity of the pressure of mixed gases).

He proposed a hypothesis in which there is a force of repulsion specific to each distinct type

of atom (simple or compound), and where each type of atom was immune to the repulsive

forces of other types. Since each distinct fluid pushed against the containing surface with its

own force of repulsion, the various forces of repulsion present in any container merely added

together to produce a total pressure (1801, 242-43; 1802, 536). This same hypothesis also

explained why gases in mixtures do not separate out according to their specific weights.

According to the hypothesis, the particles of each distinct type in a given volume arranged

themselves independently of all other types in the same volume, as if the other types were not

present at all. Later, when Dalton noticed that different gases had different solubilities in

water, he rejected this theory for a caloric theory of repulsion in which particles of different

types had different sizes as well as weights (see Dalton 1805, 286).

We still might wonder, however: what is it that causes two particles to combine?

Why should two particles combine, rather than remain separate? Needham objects to the fact

that “Dalton offers no account of what draws unlike atoms together in molecules” (2004b,

1046). It is true that Dalton gives us very little indication of the nature of chemical

combination. Dalton merely hints that, if two bodies are to combine, they must be “disposed”

to do so, and must be present in the appropriate proportions (see Dalton 1808, 192; 1808,

213). It seems then, if we dare to read between the lines, that the “disposition” of a chemical

substance to combine with another is an inherent chemical property of that substance. If so,

such a disposition, particular to each type of atom, would be no more (or less) mysterious

than Newton’s gravitational force.6

I do agree with Needham that there is a sense in which Dalton’s explanation of

chemical combination is less than satisfying. Although Dalton distinguished between

chemical and mechanical effects, he did not explain the nature of chemical combination or

any underlying reason for the “disposition” of one substance to combine selectively with

certain other substances in precise ratios. Furthermore, the meager account that Dalton

provided for chemical combination gave no ability to predict which kinds of atoms might

have the tendency to combine, and in what arrangements and proportions they might do so.

However, I believe that these problems are reasons for withholding acceptance of Dalton’s

theory, not for denying that his theory was explanatory. (I will discuss this point more in

Section 4.)

6 That Dalton would have been happy with such an explanation is supported by the

fact that he had the goal of giving a Newtonian account of chemistry in which everything was

based on forces of attraction and repulsion among particles (see Dalton’s 1810 lecture notes,

reproduced by Roscoe and Harden (1896, 13-15)).

Dalton’s theory thus explains several facts about fluids known at the dawn of the nineteenth

century: constant and multiple proportions; the difference between compounds and solutions;

and why chemical combination requires constant proportions of elements, while mixtures do

not.

3. Duhem’s chemical equivalents. In his 1914 work The Aim and Structure of Physical

Theory, Duhem argues that physical theory, if understood as having the goal of explanation,

is subordinate to metaphysics and depends on the metaphysical system that one adopts.

Due to the sensitivity of explanation on metaphysical and philosophical positions, Duhem

holds strongly to the view that explanation should be relegated to the realm of philosophy

and metaphysics. Therefore, according to Duhem, explanation should not be a part of

physical science; the true aim of physical theory is not to explain, but to give a “system of

mathematical propositions, deduced from a small number of principles, which aim to

represent as simply, as completely, and as exactly as possible a set of experimental laws”

([1914] 1954, 19).

Duhem claims that there is no way of overcoming the irreconcilable metaphysical

differences between the atomist and non-atomist camps, and that even among atomists there

are deep metaphysical disagreements (see Duhem [1892] 2000, 167-168). So a chemist,

when acting as a scientist, should not meddle in debates over atomism; philosophy and

science are two completely separate enterprises, and science is not in the business of

providing explanations. Duhem’s view about the non-role of explanation in science has a

large impact on the shape of his chemistry.

3.1. Duhem’s anti-atomistic chemistry. In 1892, Duhem published an essay entitled

“Atomic Notation and Atomistic Hypotheses”. The essay is a fascinating account of how

chemistry can be done without atoms, and how, furthermore, the entire history of the science

can be told without atoms. The essay concludes with a warning against taking atomistic

theories of chemistry seriously.7 Here I will outline the argument of his essay.

Duhem began his description of the science of chemistry on the solid foundation of

observables: the proportional weights of the various elements in chemical compounds, and

“they alone…represent the experimental givens of chemical analysis” (Duhem [1892] 2000,

130; emphasis mine). Derivative from these proportional weights are the proportional

numbers that chemists choose, by convention, to assign to each element. In order to establish

these conventions, chemists collate the many instances in which a particular element (e.g.

nitrogen) is found in a compound and note that its proportional weight in these compounds is

generally very close to a small multiple of a particular whole number (e.g. 14 for nitrogen).8

7 Duhem ([1902] 2002) is a similar, although slightly more lengthy, form of this argument.

8 As the nineteenth century progressed, evidence began to show that the multiples of whole

numbers were not small for all compounds, which led to some doubt in Duhem’s mind about

the law of multiple proportions (see Section 3.2 below).

The collection of instances of a given element in compounds, together with a consideration

of the analogies between the various compounds to which the element belongs and other

compounds, helps chemists to collectively fix the most reasonable standard of equivalent

weights of various elements. With a system of equivalent weights in place, crude chemical

formulas with symbols and superscripts take on a particular meaning; the letter-symbol for

each element represented the equivalent weight of that element, and the superscript in the

formula represents the number of “equivalents” represented. An “equivalent” for Duhem is

simply a certain amount, by weight, of an element in proportion to the weight of other

elements making up a compound.

A study of analogies among various chemicals and the way in which some elements

substitute for others in analogous compounds allows for refinement of crude formulas;

refined formulas express not only the number of equivalents for each element, but also group

the symbols in such a way as to make apparent the more basic (and substitutable) parts of the

compound. For example, the crude formula for alcohol is C2H6O, but if we wish to regard

alcohol as water in which an equivalent of hydrogen is replaced by an ethyl group (C2H5),

then we might represent alcohol by the formula (C2H5)HO ([1892] 2000, 149).

Even more subtlety in representation was needed as it was realized that certain

elements or basic subgroups could be swapped not only one-for-one in analogous compounds,

but also two-for-one or three-for-one. For example, the PO group is substitutable for three

equivalents of hydrogen in HCl or H2O ([1892] 2000, 156). The notion of valency was

introduced to provide a method of accounting for interchangeable groups. Consideration of

each element’s involvement in various compounds and subgroups led to a standardization

(with some exceptions and uncertainties) of valencies for each element. Constitutional

formulas were instituted, in which connective lines indicated the number of valencies that are

“exchanged” among elements. Using this notation, Duhem showed that all of the

relationships in a compound could be shown at once, and thus all of the derivative properties

of these relationships were evident at first glance (see figure 1). This representation was an

improvement over both crude formulas and refined formulas, in which either no subgroups

were shown or some subgroups were emphasized at the expense of hiding others.

Figure 1. Duhem gives the example of the constitutional

formula for potassium nitrate (a), which contains enough

information for generating any of the refined formulas (b), (c),

or (d), which each emphasize different analogies with other

compounds.

After explaining the developments that led to the system of constitutional formulas,

Duhem explained that, although it is tempting to view the constitutional formulas as

representing the atomic structure of a molecule, it is not necessary to do so. Under his

interpretation, these formulas merely encode two types of information: (1) how many

O

O

N O K

(a) (b) (c)

NO³ K

(d)

NO²

O

K

N O²

OK

equivalent weights of a given element are present in the compound; and (2) how many

valencies are exchanged between pairs of elements. Duhem is very careful and pointed in his

use of the word “equivalents” instead of “atoms”, and his use of the word “valency” instead

of “atomicity”. He believed that all of chemistry at his time (including classification of

chemicals and prediction of their properties) could be done without reference to atoms.

3.2. Duhem’s resistance to the atomic interpretation. Although Duhem avoided all

mention of atoms when writing as a chemist, he had no qualms about passing a verdict on

atomism when writing as a philosopher interpreting chemistry. In fact, Duhem spent a large

segment of his 1892 article—a total of 11 pages—discussing how well (or how badly)

atomistic theories explain. By the time he wrote, chemical atomism had expanded to include

a great many addenda and modifications on Dalton’s original basic postulates. Duhem had

several complaints about the inconsistencies and problems with these addenda, but of

Dalton’s original basic theory, he had only praise for its explanatory power. Duhem showed,

in fact, that the “fundamental laws of chemistry” can be deduced from chemical atomism,

including the law of definite proportions, the law of multiple proportions, and the “law of

isomorphism” (i.e chemical analogy due to similarities in molecular structure) (Duhem

[1892] 2000, 169). Admittedly, Duhem never said explicitly in his comments on Dalton’s

atomism that the theory explained chemical phenomena. But he did refer to the atomic

theory as a “plausible and appealing interpretation” of the law of multiple proportions

(Duhem [1902] 2002, 93), and he also applauded several other explanatory features of

Dalton’s theory. In addition, Duhem makes it extremely clear that atomism is a metaphysical

and interpretive position, which in his philosophy of science is tantamount to placing it in the

realm of explanation (not the realm of science itself).

But what of Duhem’s critiques? At the end of the passage in which he discussed the

strong points of Dalton’s theory, Duhem concluded with the following words: “This is

Dalton’s atomic hypothesis. It agrees well with the primary laws and the primary notions of

chemistry. The concern now is to complete it...” ([1892] 2000, 170). It is here that Duhem

began to take issue not with Dalton, but with Duhem’s own contemporaries who attempted to

give atomic explanations of chemical combination and atomicity (a.k.a. valency). He had

three main objections:

(1) No viable explanation has been given for the atomicity property of atoms, and thus it

is difficult to explain chemical combination (i.e. what holds atoms together). Also,

atoms of the same element do not always have the same atomicity for all compounds

into which they enter (see Duhem [1892] 2000, 171-173; [1902] 2002, 88-91).

(2) There are compounds with very different formulas that have very similar macroscopic

shape and properties. This is a problem if compositional formulas are taken to

represent the arrangement of atoms in a molecule (see Duhem [1892] 2000, 175-

176).9

9 Interestingly, this objection is present in Duhem ([1892] 2000) but absent from Duhem

([1902] 2002).

(3) After Dalton, some compounds were found to require large (rather than small) whole-

number ratios of masses, which opened up the possibility that the law of multiple

proportions is only trivially true. To make matters worse, Duhem showed that the

law of multiple proportions, which is the strongest evidence for atomism, can never

be empirically verified. No measurement technique can ascertain the exact ratio of

the masses of two elements in a compound; it can only say that the ratio lies within

certain limits. Because there is infinity of possible numbers—both commensurable

and incommensurable—within these limits, there is a possibility that the true ratio is

actually incommensurable (see Duhem [1902] 2002, 92-93).10

After discussing the above problems in some depth, Duhem concluded, “it is apparent that

the atomic notation as ordinarily explained faces certain difficulties which have their source

in experience” ([1892] 2000, 176). It appears that Duhem’s main reason for his rejection of

atomism (as a philosopher) was not that it was an explanation, or that it didn’t explain

anything, but that it didn’t explain well enough to be accepted as an interpretation of

chemistry.

10 Duhem recognized this objection to atomism as a weak one. If one is to attack atomism via

the law of multiple proportions, he cannot do so without bringing down some of the most

basic concepts (e.g. valency, constitutional chemical formulas) on which the entire edifice of

chemistry is based (see Duhem [1902] 2002, 93).

4. Explanation vs. acceptance. Now, after examining the cases of these two historical

chemists who had such opposite views—both on chemical atomism and on explanation in

science—can we say anything interesting about the relationship between the explanatory

status of a scientific theory and acceptance of the theory?

First, I would like to point out is that explanatoriness is not a binary question.

Explanation admits of degrees of satisfaction. I have shown that Dalton’s theory was

explanatory of many phenomena in chemistry at his time, but I have also admitted a sense in

which it was less than satisfactory. I have also noted Duhem’s acknowledgement that

Dalton’s theory is explanatory in part, but not explanatory enough to account for all of the

chemical phenomena that were known at the end of the nineteenth century.

Secondly, we see in Duhem’s case that it is perfectly possible to admit that a theory is

explanatory of a set of phenomena but not accept the theory. This is not very surprising. It

is easy to admit, for example, that caloric provided a good explanation for many phenomena

related to heat while not accepting the caloric theory of heat. In Duhem’s case, his rejection

of atoms was motivated by the set of phenomena that he felt atomism could not explain. This

motive seems to generalize. Our reluctance to accept the caloric theory comes from the fact

that there are phenomena that this theory does not explain. There is some kind of threshold

here; for us to accept a theory, it must be explanatory enough.

I think there is something interesting we can say about this threshold. Our standard

for how high the bar must be set will be relative to the amount of time and effort that has

gone into attempting to fill out the explanation. When a theory is first proposed, we tend to

be more forgiving of the things that it cannot yet explain, or the aspects of the theory that are

less than satisfying in an explanatory sense. Take Berzelius, for example. Even though he

was reluctant to accept Dalton’s atomism wholeheartedly, he still thought it a worthwhile

research project to investigate how chemical combination of atoms might occur (see Rocke

1984, 66-78). Duhem, working as a chemist nearly a century after Dalton, found it difficult

to forgive chemical atomism for the important phenomena that it had not yet succeeded in

explaining. He was frustrated with the pseudo-explanations of chemical combination and the

vague concept of atomicity that offered nothing more than the non-atomic concept of valency.

He believed that since such explanations had not been advanced since the time of Dalton,

there was not much reason to believe that they would be forthcoming in the future.

I have attempted to show in this paper that Needham is wrong about the explanatory

worth of Dalton’s theory and also about Duhem’s assessment of it. But I think there may be

a deeper and more crucial difference between my position and Needham’s position: it seems

to me that for Needham, acceptance of a scientific theory and that theory’s explanatoriness

go hand in hand. I disagree. I think that the relationship between holding a theory to be

explanatory and accepting the theory is somewhat more loose. It is perfectly legitimate to

acknowledge the explanatory power of theories we do not accept, and even to acknowledge

the explanatory power of incomplete theories that still leave some details to be filled in. Still,

explanatoriness and acceptance seem to be related by a threshold function that increases its

standards with time.

My position is that it was Dalton’s acceptance of his atomic hypothesis, and not his

claim that it is explanatory, that was somewhat naïve. Dalton did, in my opinion, have a

particularly low threshold for theory acceptance. There were enough problems and

unresolved details in his chemical atomism that would have probably given me pause to

accept it if I were one of his contemporaries. However, I would not have called it non-

explanatory.

References

Dalton, John. 1801. “New Theory of the Constitution of mixed Aeriform Fluids, and

particularly of the Atmosphere.” Journal of Natural Philosophy, Chemistry, and the

Arts 5 (October): 241-244.

Dalton, John. 1802. “Experimental Essays On the Constitution of mixed Gases … and on the

Expansion of Gases by Heat.” Memoirs of the Literary and Philosophical Society of

Manchester Vol 5, Pt. 2: 535-602.

Dalton, John. 1805. “On the Absorption of Gases by Water and other Liquids.” Memoirs of

the Literary and Philosophical Society of Manchester, 2nd Ser., Volume 1: 271-287.

Dalton, John. 1808. A New System of Chemical Philosophy, Vol. I, Pt I. Manchester: R.

Bickerstaff.

Duhem, Pierre. [1892] 2000. “Atomic Notation and Atomistic Hypotheses.” Foundations of

Chemistry 2: 127-180. Translated by Paul Needham. Originally published as

“Notation atomique et hypotheses atomistiques,” Revue des questions scientifiques

31:391-457.

Duhem, Pierre. [1902] 2002. “Mixture and Chemical Combination: An Essay on the

Evolution of an Idea.” In Paul Needham (ed. and trans.), Mixture and Chemical

Combination And Related Essays, 1-118. Dordrecht: Kluwer Academic Publishers.

Originally published as Le mixte et la combinaison chimique: Essai sur l’évolution

d’une idée (Paris: C. Naud).

Duhem, Pierre. [1914] 1954. The Aim and Structure of Physical Theory. Translated by Philip

P. Wiener. (Princeton: Princeton University Press). Originally published as La

Théorie Physique: son Objet, Sa Structure, 2nd Edition.

Needham, Paul. 2000. “What is Water?” Analysis 60 (265): 13-21.

Needham, Paul. 2004a. “When did atoms begin to do any explanatory work in chemistry?”

International Studies in the Philosophy of Science 18:199-219.

Needham, Paul. 2004b. “Has Daltonian Atomism Provided Chemistry with Any

Explanations?” Philosophy of Science 71:1038-1047.

Needham, Paul. 2008. “Resisting Chemical Atomism: Duhem's Argument.” Philosophy of

Science 75:921-31.

Rocke, Alan J. 1984. Chemical Atomism in the Nineteenth Century: From Dalton to

Cannizzaro. Columbus: Ohio State University Press.

Roscoe, Henry E., and Arthur Harden. 1896. A New View of the Origin of Daltonʼs Atomic

Theory: A Contribution to Chemical History. London: MacMillan and Co.