Mr. De la Rue on Cochineal. 489 



This mean corresponds perfectly with the formula 

 C,6H5N3 0i8 + 2Aq, 

 as may be seen by a comparison of the theoretical and expe- 

 rimental numbers. 



Theory. Experiment. 



f ^ 1 Mean. 



1 equiv. dry acid ... 287 94*10 94*04 



2 ... water .... 18 5*90 5*96 

 1 ... crystallized niO 3^^ ^^^,^^ ^^^^.^^ 



trococcusic acid . .J 

 Properties of Nitrococcusic Acid. — It is of a yellow colour, 

 crystallizing in rhombic plates, and presenting very different 

 aspects, according to the circumstances under which it is cry- 

 stallized. Its solution stains the skin yellow, it is soluble in 

 cold, but considerably more so in hot water; soluble in al- 

 cohol, and very soluble in aether. All its salts dissolve readily 

 in water, and most of them in alcohol ; it deflagrates violently 

 on being heated ; it dissolves iron and zinc, becoming dark- 

 coloured. It is decomposed by sulphuret of ammonium with 

 separation of sulphur and the formation of the ammonia salt 

 of a new acid, which I have not yet examined. 



Compounds of Nitrococcusic Acid. 



Nitrococcusate of Potash. — I have prepared this salt by 

 two different methods. 



a. A solution of nitrococcusic acid in boiling water was 

 accurately saturated with carbonate of potash ; by evaporation 

 to a small bulk and cooling, the salt was obtained in small 

 yellow crystals ; it was purified by draining and recrystallizing. 



b. An aetherial solution of the acid was precipitated by the 

 cautious addition of an alcoholic solution of potash ; the pale 

 yellow precipitate washed with aether and dried, then dissolved 

 in as small a quantity of cold water as possible, and the solu- 

 tion poured into about five times its bulk of absolute alcohol ; 

 after standing some time the salt crystallized in well-formed 

 crystals ; it was washed with aether and dried. The aetherial 

 washings being added to the mother-liquor, a further portion 

 was obtained and washed with aether. The latter process is 

 less troublesome than the process a. 



I. *5469 grm. (a) dried at 100° C. were dissolved in a small 

 quantity of boiling water and decomposed by sulphuric acid ; 

 dried in a water-bath, the nitrococcusic acid, removed by aether 

 and the residue ignited, gave '2606 grm. sulphate of potash. 



IT. *4383 grm. [b) dried at 132° C. gave -2103 grm. sul- 

 phate of potash. 



III. '6251 grm, {b) dried at 100° C. and burnt with chro- 



