1823.] Acids in Mineral Substances. 385 



the carbonate of soda or potash, with which it has been fused 

 after saturation by acetous acid, forming or not forming a preci- 

 pitate 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 diffi- 

 culty. 



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 pro- 

 duced, 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 deoxidate 

 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 Rochellesalt, or by cream 

 of tartar. 



2. Muriatic Acid. — I have likewise discovered a test of chlo- 

 rine, 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 independent of light, and which has not 

 been attended to by chemists, is produced. The chlorine in a 

 tear, in saliva, even in milk, maybe thus made evident. When 

 the quantity of chlorine in a liquor is very small, a bit of sulphate 

 of copper placed in it on the silver is preferable to a solution. 

 To find chlorine in milk, I put some sulphate of copper to it, 

 and placed a small piece of bright silver in the mixture. 



3. Phosphoric Acid. — The alkali containing it, after satura- 

 tion by acetous acid, gives a sulphur-yellow precipitate with 

 nitrate of silver, which no other acid does. The precipitate 

 obtained with lead crystallizes on the blowpipe. M. Berzelius's 

 elegant method of detecting phosphoric acid is universally 

 known. 



4. Boracic Acid. — Its presence in carbonate of magnesia, and 

 in some other of its compounds, is indicated by -the green colour 

 they give, during their fusion, to the flame of the lamp. 



M. Gay-Lussac has observed that a solution of boracic acid in 

 an acid changes the colour of turmeric paper to red, like an 

 alkali.f Borax, to which sulphuric acid has been put, does so, 

 and the same is of course the case with a bead of soda containing 

 boracic acid. 



The most certain test of boracic acid in a soda bead, &c. is to 

 add sulphuric acid to it and then spirit of wine, whose flame is 

 coloured-green, if boracic acid is present. 



* Annals of Philosophy for July, 1820. 



+ Annales de Chimie et de Physique, tome xvi. p. T5. 



New Serie$, vol. r, 2 c 



