WRITINGS OF JAMES SMITIISON. 83 



As the carbonates of soda and of potash precipitate all the 

 solutions of earths and metals in acids, so do they decom- 

 pose all their salts by fusion with them. Fusion with car- 

 bonate of soda or potash affords there a general method of 

 separating acids from all other matters. 



Lead forms an insoluble compound with all the mineral 

 acids except the nitric. It may consequently be imme- 

 diately known whether a mineral does or does not contain 

 an acid element by the carbonate of soda or potash, with 

 which it has been fused after saturation by acetous acid, 

 forming or not forming a precipitate with a solution of lead. 



If the production of a precipitate proves the presence of 

 an acid, the determination of its species will present no great 

 difficulty. 



1. Sulphuric Acid. If the alkali which has received it 

 from the mineral is fused on charcoal, and then laid in a 

 drop of water placed on silver, a spot of sulphuret of silver 

 will be produced, as I have stated on a former occasion.* 

 Bright copper will likewise serve for this purpose. 



Fusion in the blue flame will often be sufficient to deoxi- 

 date the sulphur. 



It is needless to observe that the alkali used in this trial 

 must itself be perfectly free from sulphuric acid. When 

 such is not possessed, its place may be supplied by Rochelle 

 salt, or by cream of tartar. 



2. Muriatic Acid. I have likewise discovered a test of 

 chlorine, and consequently of muriatic acid, of delicacy 

 equal to the foregoing. If any matter containing chlorine 

 or muriatic acid is laid on silver in a drop of solution of 

 yellow sulphate of iron, or of common sulphate of copper, 

 a spot of a black chloride of silver, whose colour is inde- 

 pendent of light, and which has not been attended to 'by 

 chemists, is produced. The chlorine in a tear, in saliva, 

 even in milk, may be thus made evident. When the quan- 

 tity of chlorine in a liquor is very small, a bit of sulphate 



* Annals of Philosophy for July, 1820. 



