ACTION ON CERTAIN CHEMICAL REAGENTS. 
203 
Hydrosulphuric acid produced a precipitate in l-30,000dth. 
Ammonia nitrate of silver formed a yellow precipitate with 
l-30,000dth ; with a more diluted solution, the color of this 
precipitate was not sufficiently apparent. 
III. The sensibility of reagents for metals and their 
oxides. 
For free alkalies in general. — Turmeric paper detected 
the presence of l-3000dth caustic alkali. 
Paper stained with red cabbage, detected the presence of 
l-7500dth of caustic alkali. 
Brazil wood was colored slightly violet, with l-20,000dth. 
Litmus paper reddened by acetic acid, was distinctly 
rendered blue by 1-S0,000dth. 
Hydrate of potassa contains 16 per cent, of water, therefore 
the quantity of real potassa detected by the above agents, was 
l-3600dth, l-9000dth, l-24,000dth and l-95,000dth. 
For Potassa. — An alcoholic solution of chloride of plati- 
num, occasioned a precipitate in a solution of nitrate of potassa, 
containing 1-206 of this base; a solution containing l-200dth 
was not precipitated by it. 
A very concentrated solution of tartaric acid, produced a 
precipitate with l-220th, but none with l-230th. The sen- 
sibility of the reagents was tried at 59° Fahr. 
For Lime. — Oxalate of ammonia produced a cloudiness 
after a few minutes, in a solution of chloride of lime, contain- 
ing l-400,000dth of lime. 
For Baryta. — Fluo-silicic acid produced a slight precipi- 
tate in solution of chloride of barium, containing l-3800dth of 
baryta. 
A solution of sulphate of soda produced, in half an hour, a 
cloudiness in a solution containing l-71,000dth. 
For Magnesia. — A solution of phosphate of soda, indicat- 
ed in 24 hours, the presence of l-200,000dth of magnesia, in 
a solution of sulphate of magnesia. This reagent must be 
very concentrated, and a quantity equal to the solution ex- 
amined, must be added. These conditions are absolutely 
