On'iheProduBisnofartiftcial Cold. 275 



Muriate of lime produces no effe£i upon tin or japanned veflel.s ; hence the apparatus is 

 bed made of common block-tin -, obferving that the tube and cup be made of the thinneft 

 tinned iron, and the whole befidcs of the fame fubflance, but confiderably thicker. * 

 ' The tube and cup fhould be very fmooth within-fide, and perfe£l!y centra! \ the tube having 

 as little feam as poffible, that the grindinj; inftrament be not obftrudted.' 



The grinding inftrument afts bell- when tl>e edge, inftead of being quite horizontal, is a 

 little inclined from each fhoulder, towards the centre. 



> In order to keep this paper within tolerable limits, I have carefully avoided a repetition of 

 all matters mentioned in my former papers on this fubjeft} I mud therefore refer to thofe, 

 efpecially that " On the bed Methods of producing artificial Cold," f for the particular 

 mode of conducing experiments on cold ; this being eflentially the fame in principle, 

 whatever be the materials made ufe of to effe£l: it. Hence, the apparatus jud defcrlbed is 

 applicable to ihc ufe of the mineral acids, X as well'as fo that of muriate of lime ; recolleiling 

 that it is neceflary to fubditute glafs for tin, when the former are ufed ; or to give the infide 

 of the cup, or veflel containing it, a coating of wax, to defend the tin from their 

 aftion. 



Having given an account of Fr. Lowlt's experiments on the power of muriate of lime 

 for producing artificial cold, and added fuch obfervations of my own as refulted from them, 

 I fliall conclude by exhibiting a general view of the different frigorific mixtures compofed 

 of chemical fubdances with ice, as I have before done, (Phil. Tranf. for 1795, page 279,) 

 of thofe in which the ufe of ice is difpenfed with. 



* The belt method of conftrufling veffels for the purpofe of excluding heat," isobvioufly to have them 

 ijiade of the beft nnn-condufting fubftance, lined within with the bcft conducing fubllance j hence thefe 

 veffels (the tube excepted) might be fitter for the purpole, if made of wood lined with tin. 



My general rule for conftrufting the apparatus, is to allow _/o«r times, by meafure, the water to be frozen 

 and reduced to powder, in the capacity of the tube that is to contain it; and three times the weight (by 

 meafure) of the muriate of iirae, to the cup in which the muriate of lime is to be cooled, and the ice-powder 

 afterwards added to it : and, when nitrous acid is ufed, (inftead of muriate of Iime,)/««r times its vveight j 

 and about four times the diameter of the velTels to that of the tube. 



The preparatory mixtures, that is, fuch as are ufed for cooling the material* previoufly to mixing, art beft 

 made of ice and falts; thefe retaining their temperature longer than thofe confifting of folutions of falts lA 

 water or acid ; but, in either cafe, if neceflary, they may be occafionally renewed, after the water is becomi 

 folid. 



+ Phil. Tranf. for 1795, p. 270. 



J Nitrous acid, and vitriolic acid, may at any time be immediately procured from a chemift's fliop ; 

 whereas the muriate of lime, not being ufed for any other purpoft?, tiiuft commonly be prepared for this 

 ^lone; hence it may not unfrequently happen that rfie former, on this account, may be preferred. 



N n Ji Class 



