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attention almost entirely tothe difficult formsof labour, I have not had much opportunityof remarking, in many cases, those indica-tions which, in natural labour, foreshow itsprobable duration. I may observe, however,generally, that the more the previous chil-dren, the more speedily labour proceeds.Cœteris paribus, the larger the pelvis, themore rapid ; the smaller the pelvis, themore tardy the delivery. Where the softer

parts are relaxed, the delivery is faoihtatpd ;and where they are rigid, it is delayed.Much depends upon the efforts of the woman.In some women the efforts are sluggish ;in others they are very violent. Much alsodepends upon the state of the os uteri ; andif you find it wide open, thick, soft, andyielding, where a woman is of the ordinarysize, and the womb is active, and there have ebeen children before, the head descendsquiciJy enough ; but if the disc of the osdo not exceed the breadth of a shilling, be-ing thin, unyielding and contractéd, thenparturition is not so speedily accomplished.

Morbid Symptoms.—In the progress ofabours, such as I have described, thereare various morbid symptoms, not, indeed,of much importance, yet not to be over-looked altogether. When the child is aboutto enter the world, tenesnius is felt for areason 1 explained to you yesterday, name-ly, in consequence of the bearing of the Ihead on the sacrum, perinæum, and rectum.Micturition will also take place, principally,I suppose, from the pressure of the child’shead on the neck of the bladder, and irt thecommencement of the labour ; this requiresno remedy, but you ought to leave the roomoccasionally. Cramps are likely to be pro-duced from pressure on the obturator andsciatic nerves, and in a natural labour, an at-tack of the cramp is generally favourable ;the child being sometimes born soon afterthe cramp comes on, as it occurs principallywhen the head of the child is rapidly de-scending. Again, in natural labours youhave Vomitings occurring during the first

stage, and scarcely requiring a remedy. Ifmedicine be necessary, the effervescingdraught is, perhaps, the best. Four scruplesof citric acid mav be dissolved in four ouncesof water, and ’five scruples of carbonatepotass in four ounces of water, and a tablespoonful of each of these when effervescing,maybe given every quarter or half hour, tillthe vomitings cease. Very severe rigors andshiuers are felt, with which, if you were un-acquainted, you might be alarmed, womensometimes shaking as if they were in an

aoue fit. If this be followed up by symp-tcms of pyrexia, fever is to be feared if bysevere pains in the head and abdomen, evi-dently not proceeding from the labour, thenyou may suspect that there is inflammation.If there be much flushing of the face, throb- i

bings of the carotids, and the pulse high,you will have reason to apprehend thatconvulsions may supervene. In such cases,abstract blood ; twenty, or five. and-twenty,ounces from the arm. These accidents,however, are rare : in general, where youhave these symptoms, without the other

signs of fever, inflammation or convulsions,they are not to be viewed as alarming, butas auspicious, as they seem to indicate thatthe labour will be active, and its termi-nation speedy.

Having said thus much, Gentlemen, re-specting the phenomena of natural labour,1 had intended to pass on to the duties ofthe accoucheur, but as our time is expired,I shall reserve this till our next meeting.

LECTURES ON CHEMISTRY,

BY

PROFESSOR, BRANDE.

Delivered at the Royal Institution of GreatBritain.

LECTURE XIV.

On the Simple Supporters of Combustion.

GENTLEMEN,—We have now to examine aclass of substances possessing very ener-getic powers of combination, with simpleinflammable bodies capable of producingacids, and which, when submitted to electro-chemical decomposition, are attracted bythe positive pole; they are therefore calledelectro-negative supporters of combustion,and are three in number, namely, oxygen,chlorine, and iodine.

Now, first, of oxygen, a substance of thegreatest importance in vegetable and animallife, in the formation of water, and, in pointof fact, recent chemical experiments havetaught us that it forms, perhaps, nearly theone half of the substances of our globe. Itwas discovered by Dr. Priestley in 1774,and I mention this date particularly, be-cause, although a number of factitious airshad been discovered, none of them had beenfound capable of supporting combustion; =and you may judge of Dr Priestley’s sur-prise, when he put a lighted candle into it,and found that it burned with greater bril-liancy than before, and that a mouse whichhe put into it, lived three times as long as itwould in any other gas. Dr. Priestley ob-tained it by heating the red oxide of mer-

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cury, and he found that the mercury re-turned to its metallic state, and that a quan-tity of gaseous matter escaped ; this hecollected, and found to be oxygen, or, ashe called it, dephlogisticated air. It may beobtained by heating red lead and nitre in thesame way, but the black oxide of manganeseis the substance generally resorted to in thelaboratory. If you wish to obtain the oxygenpure, you take the salt called chlorate ofpotash, and heat it to redness in a glassretort. You see the operation here goingon ; the salt is put in a powdered state intoa retort, and when the retort is made almostred hot, the gas is given off in great abun-dance in a pure state, but the expense ofthis salt is the chief impediment to its use.For common purposes, you may obtainlargequantities of oxygen from common saltwhen very much heated, but the gas notvery pure. You will observe the mode em-

ployed for collecting gases in general; bot-tles are filled with water, and then invertedin a trough; as the gas enters the vessel,the water is displaced, and this is the wav inwhich all these gases are collected, whichwhich all these gases are collected, wlichare not soluble in water ; but, for the col-lection of such as are soluble in that fluid,we employ mercury. This is called the

hydro-pnemnatic trough, and the whole of. theapparatus is called the hydro-pueunaatic ap-paratus, and we are chiefly indebted to Dr.Priestley for the mode of collecting gases inthis way. If a large quantity of it shouldbe required, we may use with great ad-vantage a wrought-iron bottle, which maybe put into the fire, and to the top of whicha flexible tube may be attached by a joint;but when you wish to obtain oxygen for

any nice purpose, you must use the chlorateof potash. Sometimes it is inconvenient tobeat the oxide of manganese red hot, andthen the gas may be obtained by distilling itwith sulphuric acid ; this is not, however,a very commendable process. You are tomix the oxide of manganese with the acid,and make the mass into the consistence ofa thin paste, and apply your heat at first

gently. Now, of course, in all these cases,the retort contains a quantity of commonair, and therefore we generally suffer thisportion to escape, and begin only to collectthe gas, when we think it is coming overpure. Earthenware retorts are sometimes

employed, as are also those of glass. Mostof our glass is fusible, and melts readily,from containing lead, when exposed to hightemperatures ; but there is a sort of glassmade at Newcastle without the oxide of’

lead, and therefore bears a very high tem-perature without fusing ; but for ordinarypurposes, we find the common glass retortscased with a mixture of sand and clay tobear a very great degree of heat, withoutbreaking or melting. You should be fur-

nished with receivers of different kinds;some of them should be furnished with

stop cocks, and be graduated; you shouldalso be provided with tubes of different

sizes, nicely graduated and divided into 100parts, if you wish to make any delicate ex-periments on the gases.

In subjecting gases to the action of elec-tricity, we generally use a glass tube, witha couple of wires passing through it, andyou will find that you can easily pass anelectric spark through the gas. When greatquantities of gases are to be collected, weuse vessels of this kind, which are called

gasometers. Here you see is a circular vesselopen only at the bottom, and of a little lessdiameter than that in which it is inverted;this cylinder has a solid stem, which passesthrough a hole in the cross bar of the framefixed to the top of the pail ; it serves

to steady the cylinder, and to indicate the

quantity of enclosed gas, and the weight ofthe cylinder is counterpoised by a weightpassed over a pulley. A tube furnishedwith a step-cock penetrates the bottom ofthe pail or outer cylinder, and is continuedto the centre, when it meets another tube

coming from the top of the vessel, also hav ing a stop-cock, and from the plan ot’junc-ture, a tube passes directly upwards throughthe middle of the vessel, a little above thelevel of its upper rim. lnstruments of thiskind are constructed upon an immense scalein our gas-works, where the carburetted hy-drogen gas is prepared for purposes of illu.mination. Here is another instrument verynecessary in the examination of gases, it iscalled a gas-holder, and a very convenientpiece of apparatus it is. It consists of a cir.cular copper vessel, which has attached to ita small pneumatic trough, from which a tubepasses nearly to the bottom of the vessel.It should be made of copper, and not of tin-

plate : all your glass receivers should be

ground to smooth surfaces at their openings,so that when you wish to’ close them, voumay have nothing to do but to slide a pieceof ground glass over the orifices.

Now, in order to judge of the purity ofoxygen, a delicate operation is required,which will be afterwards shown ; but for or.dinary purposes, you need only to dip intoit a heated wick of a taper, but withoutflame, and if it rekindles with a snap, youmay consider that the gas is tolerably pure.It is a matter of great importance to the

chemist, to determuie the specific gravityof the gas, in reference to common air, audwe arrive at a knowledge of this eircura.stance by weighing eclual bulks of the two.Now, with regard to the specific gravity ofoxygen, it is found that one huudred cub;cinches weigh 33.75 grains, and assumingcommon air as 1., oxygen is represented by

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1.232, so that you see it is a little heavierthan common air ; and, in relation to hy-drogen, you will find that oxygen is nearlysixteen times heavier than it ; and uponthis supposition we found our numerical

representation of the weights of bodies.You have already seen with what splen-

dour the oxygen supports the combustion ofa taper. I shall now introduce some sul-

phur into the gas, which burns in the corn-mon air of the atmosphere with a dark blue flame. Having ignited the sulphur in theoxygen, Mr. Brande proceeded : you see

that the combustion is very vivid, and thatthere is at the same time a combination ofthe sulphur with the oxygen, and an acid isformed called sulphurous acid. Now, al-though I believe that all attempts to explainchemical nomenclature in the lump must beerroneous, I may just mention here, that whenoxygen enters into combination with theother supporters of combustion, or with themetals, two classes of compounds are formed,those which are not acid being usually dis-tinguished by the termination ide, as oxidesof chlorine, iron, and so on ; and such asare acid, being known by the terms oxs oric, according as the relative proportions ofoxygen, or either of the supporters of coin-bustion, may exist in the combination. Inthe present case an acid is produced, calledSulphurous acid, in order to distinguish itfrom those acids which contain a larger pro-portion of oxygen, and are therefore calledic acids. Now, there is a celebrated experi-ment, contrived by Dr. Engelhaus, to showthe union of oxygen with the metals duringcombustion, namely, the introduction of a

pin of ignited wire into a jar of oxygen, agreat light is produced, and a great numberof sparls thrown off, which are found to beoxides of the metal ; and, in short, in allthese cases of combustion of the metals, anoxide is formed with the oxygen and theignited body. You observe the iron in a stateof intense ignition ; the drops of liquid iron, even after passing through the water, are hotenough to stick to the bottom of the place,and the heat evolved generally breaks thejar in which the combustion is made, so thatwe generally select a cracked jar for the pur-pose. These experiments will suffice toshow you the power of oxygen in support-iag combustion.

The history of chemical processes willnot form a predominant part of these lectures,as I suppose that it will be better to teachyou here matters of fact rather than mattersof speculation ; but, at the same time, thereare so many curious phenomena connectedwith combustion, that it will be well tomention to you, that the phenomena ofcombustion appear in all ages to have at-tracted great attention. The first expla-

nation offered of combustion was by JeanRey in 1630 ; he found, that having melteda quantity of tin of a certain weight, andhaving kept it in a state of fusion for sometime, he ascertained that it had consider-ably increased in weight, and, reasoningupon these circumstances, he concluded

that the air had a great deal to do with it,and that a certain quantity of air had en-tered into a fixed combination with themetal, and this approaches very near to theaccount I have just given you, namely, the

fixation or union of the oxygen with thecombustible body. When the air-pumpwas discovered, it was soon found thatbodies would not burn without air; but

Rey’s experiments attracted no particularattention, until Hooke investigated the

subject, and in 1677 published an accountof his experiments, which are particularlyentitled to attention, for the skilful mannerin which they were conducted, and fromtheir singular approach to modern disco-veries. Hooke found that bodies wouldnot burn without the free access of air, andhe therefore calls the combustion of bodiestheir solution in the air. But he goesfurther than this, and he tells us, that thereis only a part of the air capable of effectingthat solution, and what is more remarkable,he tells you, that the part of the air so ca-pable of solving bodies, is precisely thesame as that which is found in a fixed state

in saltpetre ; which is nothing less than

saying, that there is a part of the air ca-pable of supporting combustion, which hetherefore calls the nitro-ætherial matter ofthe air, exactly in the sense and applicationin which we now use the term oxygen gas.Notwithstandino that this an-

proached so nearly to the truth, little noticewas taken of it, and a very different theoryafterwards prevailed until the time of La-voisier, by whom it was subverted. Stahlimagined, that when bodies burn, theythrow off a peculiar principle, which he

named phlogiston, and the theory wascalled the phlogistic theory; this plilogiston,

lie tells us, exists in all combustible bo-

t dies, and that on combustion and the forma-tion of flame depended its separation; but this explanation of the matter was at com-plete variance with the facts previouslyestablished by Rey and Hooke, namely,the increase in the weight of bodies duringcombustion. Without entering further intodetail, however, I may just mention to

you that Lavoisier, about the beginning ofthe present century, established, by a greatnumber of beautiful and correct experi-ments, a theory of combustion nearly iden-tical with that of Hooke. He showed thatoxygen is the leading principle which sup-ports combustion, and that, during combus-tion, oxygen, entered into combination with

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the burning body. This was called theFreach theory, and which until very latelygenerally obtained. Lavoisier said, thatbodies never burned without the presenceof oxygen, but we now know that com-bustion may tale place without the presenceof any oxygen whatever, and, indeed, with-out any gaseous body being present. Thenthere is the electrical theory, which I maymention, which has been lately introduced.Combustion may be, and probably is, con-nected with the electrical energies of bodies,as all bodies which act powerfully uponeach other are in the opposite electricalstates of positive and negative, and the evo-lution of light and heat may depend uponthe annihilation of their opposite state,which happens whenever they so combine.So that you observe that here an analogy isattempted to be established between com-bustion and the bringing together of twoopposite electrical states, and that com- bustion is nothing more than the aanihila-tion of their two poles. The fact is, thatwe are little acquainted with the reconditeoperations of corpuscular philosophy, andwe wish here merely to state general facts.Combustion cannot well be regarded as de-pendant upon any peculiar form of matter,but must rather be regarded as the resultof intense chemical action. So much then,for oxygen and its general properties.

Now the next elementary body on our listis chlorine, which is a substance of a veryditierent character from the preceding. It

may be readily obtained by introducing aquantity of black oxide of manganese into aretort, and l;ouring upon it three or four

partsof its weight of muriatic acid, and thenapplying heat. I shall not at present enterinto the rationale of this process, because itis rather complicated, and it will be betterexplained by and by. One of the elements Iof the acid is evolved, namely, the chlorine, I,in a gaseous form. Now chlorine may becollected over water, but cannot be longretained in a vessel containing water, be-cause it is slowly absorbed by that fluid.Chlorine is highly noxious to respiration,and therefore we do not allow any greatportion of it to escape into the air of the

laboratory : we put the apparatus under theopening of the chimney, to allow the iirst

part of the distillation to pass off, and assoon as it begins to come over of a yellowcolour we collect it. It is employed in im-mense quantities in the arts, and thereforeit is the object of the manufacturer to supplyhimself with it as cheaply as possible; hetherefore generallv obtains the chlorine froma mixture of this kind ; he takes eight partsof common salt, three of the black oxide ofmanganese, four of water, and Jve parts ofsulphuric acid. The oxide of manganese and

salt are mixed together in one vessel, andthe acid and water in another, and thenmixed carefully together. This is a veryeasy and economical mode of obtaining chlo-rine in large quantities, where it is not verynecessary to attend to its purity; the resi-.dne of the distillation is sulphate of soda,or Glauber’s salt, so that the manufacturersof the one are generally the manufacturersof the other. Now you see the gas is com-

ing- over very abundantly fiom the retort

containing the muriatic acid and the blackoxide of manganese ; but I can scarcelycaution you too strongly against its mis.chievous effects on rehpiration, fur, althoughwhen largely diluted with atmospheric airit is true that, in persons of strong lungs,it may only produce little itrillation, still Ihave known very serious consequences, in-

flammation of the lungs, and so on, pro-’ duced by it.

It was discovered by Scheele, in 1774, inthe same year in iN,Iiich oxygen was dis-covered by Dr. Priestley ; but there is a

curious part of its history relating to thediscovery of its true nature, which I maybe excused for introducing. Scheele calledit dephlogisticated muriatic acid ; he ima-gined that if he deprived muriatic acid ofits phlogiston, he obtained this gas as one

of its elements, and if you substitute for theterm phlogiston, oxygen, which they seemto have meant by it, you will find that itpresents you with not a very incorrect viewof the nature of chlorine. Berthollet ima-

gined that chlorine, or the dephlonisticatedmuriatic acid of Scheele, contained a largequantity of oxygen with the muriatic acid,and he named it, therefore, oxymuniatic acid,a term which was generally adopted by theFrench chemists. Sir Humphrey Davy af-terwards found that it did not contain oxy-geu ; he found that it was an elementarybody, and gave it the appropriate name ofchlurine, from its greenish colour, andwhether it shall afterwards be found to bea simple, or a compound body, it may alwaysretain the name of chlorine.

It has a very disagreeable smell ; its tasteis rather astringent; it supports combus-tion in some cases, with very great energy,and in others feebly. If you put a burningtaper into a jar of chlorine, it burns veryfeebly and dimly ; it burns with a reddisli

light, and is soon extinguished; on theother hand, there are other bodies whichburn in it with great splendour, and in thenext lecture I shall show you some in-stances of this kind, and explain the com-binations of this gas with oxygen.