CHEMISTRY. 



155 



Chemical trate through the ice, but will be all employed to melt 



Apparatus. 



PLATE 

 CXLI. 

 Fig. 7. 



_ Hence the quantity of ice melted ought to measure 

 the quantity of heat which has escaped out of the hot 

 body, and, of course, gives us the relative sptcific heats 

 of all the bodifs examined in this manner. The calori- 

 meter is represented in Fig. 7. It consists of three ves- 

 sels enclosed within each other. The innermost ot these, 

 ff.ff, into which the substance submitted to experiment 

 is pu't, is composed of a grating, or cage of iron wire, 

 su -ported by several iron-bars. Its opening, or mouth, 

 is covered by a lid, which is composed of the same ma- 

 terials. The middle cavity, bbbb, is intended to con- 

 tain the ice which surrounds the interior cavity, and 

 which is intended to be melted by the heat of the sub- 

 stances employed in the experiment. The ice supported 

 by the grate, mm, at the bottom of the cavity, has un- 

 der it a sieve. In proportion as the ice contained in the 

 middle cavity is melted by the heat disengaged from the 

 body placed in the interior cavity, the water runs 

 through the grate and sieve, and falls through a conical 

 funnel into a receiver placed below it. The external ca- 

 vity, aaaa, is filled with ice, to prevent any effect up- 

 on the ice in the middle cavity from the heat of the sur- 

 rounding air ; and the water produced from it is carried 

 off by the pipe ST, which shuts by means of the stop- 

 cock r. The whole machine is covered with a lid, made 

 of tin-plate and painted. 



When this machine is to be used, the outer and mid- 

 dle divisions are filled with pounded ice, well rammed, 

 and without any vacuity. The machine is then opened, 

 and the substance, submitted to experiment, being pla- 

 ced in the interior cavity, it is instantly closed. After 

 waiting till tRe body is cooled down to the freezing 

 point, the water which has run out from the middle ca 

 vity is carefully weighed. This water obviously mea- 

 sures the quantity of heat which has escaped from the 

 body experimented upon, during its cooling to the free- 

 zing point. For the various precautions employed by 

 the French philosophers, during their experiments with 

 this apparatus, to ensure accuracy, the reader may con- 

 sult Mr Lavoisier's account of them in his EIrme'.ts of 

 Chemistry, to which we have referred above. The only- 

 person in this country, who has attempted to repeat the 

 experiments of Lavoisier and La Place, was the late 

 Mr Wedgewood. In his trials a phenomenon took 

 place, which prevented him from being able to draw any 

 conclusion!) from his trials. The water which ran from 

 the nulled ice actually froze again, though the tempe- 

 rature of the ice was at 32. Such a phenomenon, un- 

 less it can be obviated, obviously makes the calorimeter, 

 ingenious as the contrivance at first sight appears, en- 

 tirely u-eless as an instrument for investigating the spe- 

 cific he t of bodies. The freezing of the water seems 

 to be owuii' tn the cold produced by its evaporation. 

 From Mi Wilson's experiment's it app<ara tliat the eva- 

 poration of ice is greatest, when its heat is 32. Now, 

 as the temperature of the water, produced by the melt- 

 ing of the ice in the calorimeter, cannot much exceed 

 32% it is obvious that a very slight diminution of tem- 

 pi-raturc by evaporation will be sufficient to begin con- 

 gelation ; and when congelation once begins, the attrac- 

 tion of the spiculae of ice formed for the particles of 

 water, will probably tend to increase the quantity of 

 ice. 



There are no other apparatus connected with heat, 

 which seem to require particular description. The con- 



trivances of Mr Leslie and of Count Rumford possess Chemical 

 great ingenuity ; but are so simple, that the reader can Apparatus, 

 find no difficulty in understanding them. ""Y"* 



CHAP. II. 

 Apparatus for Experiment* with Gases. 



THIS branch of Chemistry requires by far the most Apparatui 

 expensive and complicated apparatus. We shall satisfy for e *P c . ri - 

 ourselves with describing the most important requisites. *"^ 

 Almobt every chemical experimenter has added some- 

 thing of his own to this department of chemical vessels. 

 Hence it would be an endless and a useless task to de- 

 scribe every thing that has been proposed, or even 

 brought into use. 



1. The first requisite is a water-trough, for preparing Water 

 the gases, and for containing the vessels in which the tro g nt - 

 gases are confined. These arc of various sizes, accord- 

 ing to the extent of the laboratory, cr the objects which 

 the proprietor has chiefly in view : the largest are made 

 of wood and lined with lead, about four feet long, three 

 wide, and two deep. They have a wooden shelf fixed 

 about three inches under the surface, upon one side of 

 the trough, for holding the glass jars. This shelf is 

 perforated with holes, for the conveniency of pouring 

 the gases from one jar to another ; and these holes are 

 usually funnel-shaped, having their wide mouth at the 

 under side of the shelf. This trough, when to be used, 

 is to be filled with clean water. Water-troughs are of- 

 ten made much smaller than this. In that ca^e, they 

 are only made of tin-plate and japanned ; or what would 

 be much better, and perhaps even ultimately cheaper, 

 would be to make them of copper, which ought like- 

 wise to be japanned. A trough of this kind, two feet 

 long, sixteen inches wide, and as much in depth, with 

 a shelf soldered to one of its ends, also of copper, and 

 placed about two inches under the surface, would an- 

 swer a great variety of purposed, and, from its small 

 size, would be convenient, as it could easily be carried 

 from one place to another, even when full of water. 

 We shall give a figure of the small tinned iron water- D 



i /-.- "LATH 



troughs that are commonly used in London, a (rig. CXu. 

 8.) is a deep oblong trough, made of thin tinned iron, Fig. e. 

 well japanned, generally 18 inches long, 9 broad, and 

 14 deep. About 3iJ inches from the top is a shelf of 

 the same material, extending entirely across the trough, 

 and rather more than a third of its length. Thin shilf 

 is given inverted in Fi>r. 9. to show an oval rim project- p- ^ 

 ing from it in the centre, of which are two small holes, 

 the use of which in to secure and convey the gas into 

 any vessel set upon it, (as the bottle Fig. 8.) This 

 shelf has also two larger holes to receive two bottle sup- 

 porters. Fig. 10. and b, Fig. 8. F; j 



2. To prepare the gases, various vessels may be em- ' 

 ployed, according to the nature of the gas wanted. 

 Small retorts, with long beaks, (see Fig. 11. and 12.) Fj jj 

 answer very well ; or flunks, with bent tubes ground in- 13 14 '15 ' 

 to them. (See Fig. 13, 14, and 1.5.) 



3. To receive the gases as they came over, the most 

 simple apparatus consists of glass phials, with ground 

 stoppers, made perfectly air tight. These may be filled 

 one after another, and, the stoppers being fitted in, may 

 be placed with their mouths inverted in a vessel of wa- 

 ter, and kept till wanted ; or glass jars may be employ- 



