CHAPTER V. 



FIXING AND HARDENING AGENTS. CHLORIDES, ORGANIC 



ACIDS, AND OTHERS. 



Chlorides. 



66. Bichloride of Mercury (Corrosive Sublimate). Corrosive 

 sublimate is stated in the books to be soluble in about sixteen 

 parts of cold and three of boiling distilled water. It will 

 probably be found that the aqueous solution contains from 6 

 to 7 per cent, of the sublimate at the temperature of the 

 laboratory. It is more soluble in alcohol than in water, and 

 still more so in ether. Its solubility in all these menstrua 

 is augmented by the addition of hydrochloric acid, ammonious 

 chloride, or camphor. With sodium chloride it forms a more 

 easily soluble double salt ; hence sea-water may dissolve over 

 15 per cent., and hence th0 composition of the liquid of 

 Lang. 



The simple aqueous solutions frequently deteriorate in even a short time 

 through the formation of a pulverulent precipitate. The nature of this 

 precipitate is unknown to me, and I have been unable to find any certain 

 means of preventing its formation. Thinking that it may be due in part to 

 ammonia derived from the air, I have lately been in the habit of adding a 

 little nitric acid to my solutions, and certainly have found that they thus 

 keep much better. In any case, for work in which it is desired to obtain 

 as energetic a fixing action as possible, it is well to use only freshly made 

 up solutions. And distilled water must always be employed for making 

 up the solutions. The simple aqueous solution should give an acid reaction 

 with litmus paper, whilst that made with strong sodium chloride solution 

 is neutral. 



For fixing, corrosive sublimate may be, and very frequently 

 is, used pure ; but in most cases a finer fixation will be 

 obtained if it be acidified with acetic acid, say about 1 per 

 cent, of the glacial acid. I find that a saturated solution in 

 5 per cent, glacial acetic acid is a very good formula. VAN 



