210 W, Gibbs— Contributions to Chemistry. 
most frequently occurs in practice. The method will be appli- 
cable to all these cases if hereafter a coloring matter should be 
iscovered sensitive only to acids or bases in excess, but not pro- 
ducing specific coloration with salts which are neutral in consti- 
tution. It is possible that cyanin, the remarkable properties of 
heated in a porcelain crucible placed within a Hessian crucible 
is then while still hot to be transferred to a perfectly dry glass 
tube which can be closed with a good cork covered with tin foil. 
After cooling, the tube is weighed, the contents poured into 4 
flask, the salt dissolved in water and the copper precipita 
at a boiling heat as above. The filtrate and washings are then 
made up to a known volume. From the weight of the 
anhydrous sulphate employed the quantity of sulphuric acid 
a in the solution is known. In experiments made in t 
boratory by Mr. R. Chauvenet this method has been found 
very accurate and expeditious. 
§2. On the precipitation of copper by hypophosphorous acid. 
uate acid a hydruret of copper is precipitated, which o2 
oiling 
might be 2 ead to quantitative estimation. Experiments 
18 point have been made by Mr. R. Chauvenet with 
‘The on should be in solution as sulphate, the liquid co” 
tins ttle free acid. The ar Adres the nitrate © 
ter, the addition of the hypophosphites. In order 
= avoid the sudden evolution of Bydigen ms and also to ob 
* Bull. de la Société Chimique, 8 94. 3 
