42 Mode of preparing Sal Ammoniac. [Book VI. 



If we wifh to obtain the acid of fal ammoniac, we 

 may expel it by means of the vitriolic acid, but the 

 fumes cannot be condenfed without great difficulty. 

 For obtaining its alkali, the chemifts generally employ 

 the vegetable, as it is the cheapeft. The quantity 

 of vegetable alkali ufed is generally equal, but perhaps 

 ought a little to exceed, that of the fal ammoniac , the 

 water is in general equal in weight to the alkali, and 

 a volatile alkali fufficiently Itrong is obtained. The 

 product is different, acording to the mildnefs or cauf- 

 ticity of the fixed alkali. When a mild fixed alkali 4s 

 ufed, fo much volatile alkali rifes, that Du Hamel and 

 others thought part of the fixed alkali was volatilized, 

 and rofe along with it. This however is found to be 

 owing to the carbonic acid, which made part of the 

 weight of the fixed alkali, being transferred to the vola- 

 tile alkali. 



The fal ammoniac of commerce is in the form of 

 cakes. It is prepared at Cairo from the foot of ca- 

 mels dung, which is burned there inftead of wood. 

 This foot is put into round bottles a foot and a half in 

 diameter, terminated by a neck iwo inches high; each 

 bottle contains about forty pounds of this foot, and 

 affords nearly fix pounds of the fait. Thefe velfels 

 are expofed to the heat of a furnace/which acts on their 

 bottom, while the upper part, being cooler, fuffcrs the 

 fait to be condenfed there. When the operation, which 

 occupies three days, is finifhed, the bottles are broken 

 and the fait taken out ; it receives the form of the 

 upper part of the fubliming veffel, and the cakes 

 are therefore convex and unequal, with a protube- 

 rance on one fide from the neck of the fubliming 

 vefiel 



Pomet has defcribed . a kind of fal ammoniac in 

 loaves, firnilar to thole of fugar with the point cut off, 

 and which are imported into France by the way of 



Holland, 



