Constitution of the Subsalts of Copper. 497 



this latter mode of estimating the oxide, it being one which 

 appears to me free from objection : I would remark that the 

 residual oxide after this ignition was always examined for 

 sulphuric acid, and if any was detected the experiment was 

 rejected. The deficiency of weight between that of the salt 

 operated on and the sum of the sulphuric acid and oxide of 

 copper, was estimated as water. 



This method of estimating the water may be objected to as 

 an indirect one, but I consider it more likely to be correct, 

 where a substance possesses so simple a composition as in the 

 case of these subsulphates, than any mode would be that 

 could be devised of actually obtaining and weighing the 

 water; especially as these salts were thoroughly washed until 

 no soluble matter could be detected in the washings, and 

 dried either in a water-bath or on a porous stone, and expo- 

 sure to the atmosphere at the temperature of the laboratory, 

 50° to 80° Fahr. 



In those instances where the results of my analyses were 

 not in accordance with those cited by Berzelius, Graham, 

 Kane, Thomson and others, the examination was at times 

 repeated, sometimes thrice, and the mean of these analyses 

 taken in estimating the composition of the salt. The modes 

 of preparation and the constitution of these salts I shall clas- 

 sify in the order of their composition, and at the same time 

 notice discrepancies, when such occur, between my results 

 and those of the analysts who have preceded me. 



Trisulphate of Copper. — By boiling an equivalent of oxide 

 of zinc and two equivalents of sulphate of copper together, 

 the subsulphate noticed by Berthollet, of a bright green co- 

 lour with a shade of blue, is obtained. The mean of two ana- 

 lyses gave, from 50 grs. of this salt, 33*97 grs. of sulphate 

 barytes and 34T3 grs. of oxide of copper. The composition 

 deduced from these results would seem to indicate the for- 

 mula 2S0 3 6CuO, 3HO; but I am inclined to consider this 

 salt as really consisting of SO a 3CuO, 2HO, a constitution 

 almost exactly borne out by the second of these analyses, 

 agreeing more nearly with Brunner's analysis of the subsul- 

 phate obtained in this way, and also with the composition of 

 some subsulphates prepared in a different manner, but which 

 indicate the composition S() 3 3CuO, 2HO, which will give — 



Theory. Experiment. 



Sulphuric acid . . . 1 1'24- 11*65 



Oxide of copper . . . 33*72 34*30 



Water 504 4*05 



50*00 50*00 



By precipitating 250 grs. of crystallized sulphate of copper 

 Phil. Mag. S. 3. No. 155. Snppl. Vol. 23. 2 K 



