POKTABLE FUIINACE* 273 



^certain force, according to temperature, and tliealfadjurts the 



equilibrium, by expanding or contrafting as may be required. 



The notion of a chemical affinity fubfifting between thegafes Thefe fafts Aa 



apd vapours of different kinds, cannot at all be reconciled to "^^^^ ^^J'5^^'^'^^'^ 



thefe phenomena. To fuppofe that all the different gafes have chemical affinity 



the fame affinity for water might indeed be admitted if we ^'^^"'^^" S" ^""^ 



vapour» 

 could not explain the phenomena without it; but to go further, 



and fuppofe that water combines with every gas to the fame 



amount as its vapour in vacuo ; or in other words, that the 



elafticity of the compound fnould be exa6lly the fame as if the 



two were feparate, is certainly going far to ferve an hypothefis. 



Befides, we mufl on this ground fuppofe that all the gafes 



have the fame force of affinity for any given vapour; a fuppo- 



iition that cannot be admitted as having any analogy to other 



eflablifhed laws of chemical affinity. 



(To be continued.) 



XIV. 



Defcription of the Portable Furnace covJlru8,ed by Dr. Blacky 

 andjince improved. In a Letter from' Mr. Accum, 



To Mr. NICHOLSON. 

 Dear Sik, 



IN my Syfiem of Practical Chemiflry, Vol. II. p. 557, I Defcriptlon of 

 have given a Defcription and Drawing of a Portable Uni-J^^/°[^^^'^^^"^^^ 

 verfal Furnace, which in the praftice of my profeffion I operations, 

 found the befl furnace for all chemical operations whatever 

 Avhich require like aid. The number of furnaces which I 

 have caufed to be made for different philofophers of that 

 kind, and the ufeful hints which I have received from diffe- 

 rent quarters, have materially improved it^ that I flatter 

 myfelf, whether a defcription of this furnace would not be 

 acceptable to your readers, particularly to thofe who have 

 no accefs to the laboratory of the operative chemifl ; for 

 thofe who are familiar with pradical chemiflry will readily 

 allow% that a furnace capable of producing a very low and 

 very intenfe heat is one of the moft requifite and mofl indif- 

 penlible inflruments of all the apparatus of chemiflry. The 

 Vol. VJ. December, 1803. T great 



