Chemical Constitution of Saline Solutions. 285 
15,000 times its weight of water has no such effect. Is this due to the presence 
of free sulphuric acid in the liquid? The following experiment made with cold 
boiled chromic sulphate shows that such is the case, for potash was added in 
considerable quantity before a permanent precipitate was produced; when the 
perfectly clear liquid was filtered from any turbidity and boiled, a bulky precipi- 
tate was thrown down. When this precipitate has been washed free from all 
traces of sulphuric acid or potassium sulphate, it was dissolved in hydrochloric 
acid, and tested with barium chloride, which showed the presence of a considerable 
quantity of sulphuric acid in the substance. When a cold violet solution of 
chromic sulphate has a drop of alkali added to it, a precipitate is immediately 
formed, but this, on shaking, dissolves; repeated cautious additions of alkali cause 
the production of a green solution. 
Two experiments were made to ascertain the amount of acid liberated by 
boiling a violet solution of chromic sulphate. Three grams of the salt were made up 
to 250c.c. with water; 1th of this being taken, was boiled, and standard alkali was 
added until the production of a permanent precipitate showed itself; then a 
further addition of alkali was continued until the absence of a green tint in the 
liquor indicated the entire precipitation of the chromium. 
(1) 50 c.c. required 34 c.c. of decinormal soda-solution to give a permanent 
precipitate and neutralised altogether 60 c.c. 
(2) 50 c.c. required 34°5 c.c. and 59 c.c. of soda. 
A similar experiment was made with chromic nitrate: 2 grams were dis- 
solved in cold water, and made up 250c.c.; 50¢c.c. of this solution required 27 c¢.c. 
of the standard alkali to cause precipitation of all the metal. One-third of this 
quantity or 9c.c. were then added to 50 c.c. of the chromic nitrate solution, and on 
boiling with about a litre of water the insoluble basic compound was precipitated. 
These numbers show the fact that 56°6 per cent. of the sulphuric acid in the 
salt was liberated from the violet salt when the solution was boiled. No doubt 
temperature and the strength of the solution will modify somewhat the amount of 
acid liberated. 
The green colour is produced apparently independently of the amount of 
water in the solution, whereas, when a change of colour is owing to dehydration, 
it takes place only when at a much higher temperature after the addition of 
water. 
Again, the long continued action of an air-pump vacuum in presence of oil of 
vitriol will give the green colour even to an efflorescent salt like the chromium 
nitrate. But we find the super-saturation of acids by chromic-hydrate, and the 
addition of alkali to the violet salts, showing the same changes as that on purple 
solutions of chromium compounds, while alcohol, a dehydrating agent, has no such 
action. Water, when added to a green solution, fails to produce the change which 
TRANS. ROY. DUB. SOC., N.S. VOL. VII., PART VIII. Dn 
