On the ProduB'wn of artificial Cold. 273 



D, is the cover or lid of this veflcl, fitting over it water-tight,* forming a bottom to the 

 Veflcl, and having a rim | of an inch deep, as a (land to infulate it from the table ; the 

 whole apparatus appearing to form, when together, one cylindrical vcflel, 8 inches high, 

 and 4 inches wide.+ The veflels A and B contain each i pint and | i and the tube a, and 

 cup b, I ounce and i each. 



N. B. The drawing, with the fcale annexed, gives the feftion of this apparatus, of 

 exactly the dimenfions mentioned. The inftrument defcribed in Phil. Tranf. for J 795, 

 page 288, to be ufed with this apparatus, fliould be fo long as juft to pafs through the bot- 

 tom of the tube a, viz. -J- of an inch below it. 



Fig. 2, reprefents the /pint thermometer made ufe of in the experiments : it confifts of 

 three parts, viz. A is the thermometer, having its fcale-board (made of box-wood) of 2.femi- 

 cylindrical form, being flat in front, and round at the back, in order that it may be adapted 

 to the cylindrical tube B B, in which it Aides eafily up and down, centrally; and may be 

 occafionally taken out of it C, is a brafs ferrule, cemented to, and forming one piece with, 

 the tube, having a top or cover, which fcrews off and on. Tiie fcale extends from 100 be- 

 low o, to 100 above O; the fcale upwards being carried fo far only a8 to allow of the un- 

 avoidable expanfion to which the fpirit may be fubje£ted by atmofpheric heat. 



The thermometer (contrived by myfelf, and very accurately and neatly executed by 

 Mr. Nairne, philofophical inftrument-maker, in London,) is exaftly t-wice the dimenfions 

 of the reprefentation in the drawing, (as the fcale,) and is graduated to fingle degrees ; it 

 has a common cafe, to make it portable. 



N. B. A thermometer of the fize defcribed, is equally fit for an apparatus on a larger or 

 fmaller fcale than that reprefented in Fig. i. 



The apparatus is ufed thus. The two veflels being taken apart, ifl:. A circular piece of 

 writing-paper is cemented % over the bottom of the tube a. 2d. A frigorific mixture § is 



made 



• If this cover docs not fit water tight, jt may be made fo, by the intervention of a thin bladder pre- 

 vioudy foaked in warm water. 



■J- For the purpofe of afcertijning the proper proportion of the materials to be mixed at different temper- 

 atures, and other preparatory matters, I ufed an apparatus of the fame conftruflion as Fig. 3, Ti^b. XXIII. 

 Phil. Tranf. for 1735, but differing in having two cubes inftead of one. The dimenfions of this apparatus, 

 being adapted to the fame fcale as the former, are thus: the veffel is 5^ inches high, and \\ inches in 

 diameter ; the tubes are each -| of an inch in diameter, and 5 inches deep. The materials, being prepared 

 feparately in this veffel, were afterwards mixed in a wine-glafs. 



By means of this apparatus, in one inftance, muriate of lime put into one tube, in a liquid ftate, and 

 water in the other, were both confolidated by cold, then ground to powder, and afterwards mixed ; but the 

 fait did not grind well, and it moreover eroded and rufted the inftrument. 



J; I ule mucilage of gum arabic, or butter, if the other be not at hand ; but it is fufficient merely to dip 

 the paper in water, and apply it; the cffeft of the freezing mixture quickly cementing it. 



§ A frigorific mixture, accoiiding to the intention, may be fclefled from the table in page I.'JS of this 

 paper; or, in dcfeft of ice, from the table in page ^'79 of Phil. Tranf. for 1795. The mixture I ufe for 



Vol. v.— October 1801. Nn this 



