78 h. a. SMITH. 



polarize brightly in colours. The melting point of the crystals is 

 160° 0. (uncor.) and a crystalline mass is again formed on cooling. 

 The melting point is that of the individual crystals adhering to 

 the inner side of the tube, the melting point of the mass in the 

 tube is not sharp, and an error of two degrees might easily occur. 

 The acid is a very weak one, but it is exceeding soluble in ammonia 

 and the alkalis. It is very sparingly soluble in cold water, easily 

 soluble in hot water, in alcohol, in ether, in acetone and chloroform, 

 but it is insoluble in benzene, in petroleum spirit (even on boiling) 

 and in carbon bisulphide (slightly on boiling). 



Sublimation — The acid sublimes with difficulty and at rather a 

 high temperature, it sublimes unchanged. 



Ammonium salt — The acid is exceedingly soluble in ammonia, 

 the solution was evaporated to dryness over sulphuric acid, it 

 crystallised very well, it is not readily soluble in cold water, but 

 is so in hot water ; it does not separate out again at once on 

 cooling, thus differing from the acid itself. 



Ferric salt — The aqueous solution of the ammonium salt was 

 used, ferric chloride gives a light orange precipitate insoluble even 

 in a large quantity of water. 



Copper salt — Sulphate of copper gives a light bluish-green pre- 

 cipitate in the aqueous solution of the ammonium salt. 



Silver salt — When nitrate of silver is added to the aqueous 

 solution of the ammonium salt fine crystallisation of the silver 

 salt soon takes place, the crystals are white but become pinkish on 

 exposure to light. 



Neither barium chloride nor calcium chloride gives a precipitate. 



Solubility of the acid in water at 20° C. 



The pure acid was dissolved in boiling distilled water, and when 

 at the temperature i^iven the crystals which had separated were 

 removed by nitration ; 25-48 grammes of the nitrate gave 0*0188 

 gramme solid, equivalent to 0*0738 per cent., or the acid required 

 1,355 parts of water at 20° C. to dissolve one part of acid. 



