Chemical Constitution of Saline Solutions. 285 



15,000 times its weight of water has no such efPect. 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 250 c.c. with water; J-th 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 3-1 '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 250 c.c; 50 c.c. of this solution requii-ed 27 c.c. 

 of the standard alkali to cause precipitation of all the metal. One-third of this 

 quantity or 9 c.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 fi-om 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 



TEANS. ROT. DT7B. SOC, N.S. VOL. VII., PART VIII. 2 R 



