CHEMICAL ANALYSIS, 213 



analyfed by different chemifts, has been found to yield dif- 

 ferent proportions oF the fame ingrediants, and that the 

 difference of proportions of the conftituent parts, in many 

 cafes, is often more apparent, than real ; arifing entirely 

 from the various degrees of deficcation that has been employed 

 by different analyfts, and fometimes even by the fame perfon. 

 This point is of fuch importance, and is productive of fo 

 much trouble, that every chemiit who has analyzed a mineral 

 water, or cryflallized and feparated frnall quantities of deli- 

 quefcent falts, will at once perceive the utility of the ap- 

 paratus in this refpeft. 



This apparatus may likewife be ufed as a. ivater-bath. In The fame ufed 

 that cafe, the conical glafs veffel B is removed, and the inner ^^ ^ ^^'•" ^^^^ '• 

 tin velfei E filled with water ; into this, retorts, flalks, galli- 

 pots, vials, bottles, &c. may be immerfed for promoting the 

 proceffes of diflillation, digeftion, folution, evaporation, 8cc. ' 



or it may be ufed as z fcmd batii, {'it he'ing hard foldered) by orfmd bath, 

 filling the tin veffel with lifted fand, for performing thofe 

 operations which require a higher temperature, than that of 

 boiling water. 



When the infirument is required to be ai'ed as a freezing Method of fxetz- 



apparatus, the bottom cover G is to be taken off, and the '"S (mercury 



cavity between the interior, and exterior veffel, filled with ,\ . „^ ^ 

 ,;.... . . . ,.,,,,•, this inftrument- 



the frigormc mixture ; a wetted piece or bladder is then to 



be tied over the opening, or the cover is put on, to retain 



the mixture. The fecond frigorific material (for inftance if 



quickfilver is to be frozen) confifling we will fay, of muriate 



of lime and fnow, are to be cooled by the mixture in the 



exterior veffel, by putting the muriate of lime into the conical 



glafs veffel, together with the mercury contained in a thin 



glafs tube ; and furrounding the glafs veffel, by filling the 



interior tin veffel with fnow, or pulverized ice. When thefe 



materials have been cooled down to 0° ; the fnow and ice 



may be mixed together by emptying the muriate of lime into 



the veffel containing the fnow, and flirring the mixture with 



a glafs rod to facilitate the folution of the fait, and to produce 



the requifite degree of cold. The number of apparatus I 



have fold to philolophicalchemifls, gives me rcafon to fuppofe, 



that they have proved ufeful. 



FREDERICK ACCUM. 



,11, Old Compton Street, 



Soho. 



Letter 



