266 M. Beudant dft the Connexion hehcem [Afcitii, 



crystallizing, the form of the sulphate of copper was produced, 

 containing only 7 per cent, of sulphate of iron. 



These crystals are transparent, and of a greenish Blue ; such 

 as contain only 9 to 12 per cent, of sulphate of iron, are subject 

 to rapid alteration on exposure to the air.* 



Mixture of Sulphate of Zinc and Sulphate of Iron. 



On repeating the experiments above described, with the sul- 

 phate of zinc of commerce, containing about six per cent, of 

 sulphate of iron,f it was found that the crystal of sulphate of 

 iron was produced, with the proportion of 15 per cent, of that 

 salt ; and when only 10 per cent, was present, the zinc crystal- 

 lization prevailed. On successively redissolving the crystals thus 

 obtained, and again crystallizing, the proportion of sulphate of 

 iron in the new crystals continually increased, contrary to the 

 result obtained with sulphate of copper. 



Mixture of the Sulphates of Zinc, Copper, and Iron. 



It has appeared that the sulphate of copper requires nine per- 

 cent., and the sulphate of zinc 15 per cent, of sulphate of iron to 

 produce the rhomboidal ciystal : on continuing the series of 

 experiments in order to ascertain the proportion necessary to 

 produce the same crystal, when the sulphates of copper and 

 zinc Were both in the solution, it was found that less than three 

 per cent, of sulphate of iron was sufficient ; and the crystalliza- 

 tion took place more readily than when the sulphate of iron was 

 mixed with either of the other salts singly. It is remarkable 

 that the addition of a small proportion of sulphate of copper 

 added to the sulphates of zinc and iron should occasion this 

 change in the proportion of sulphate of iron necessary to produce 

 its peculiar crystal ; and the experiments were varied and 

 repeated, that the correctness of the results might be depended 

 upon : to 80 parts of the crystals of the sulphate of zinc of com- 

 merce, containing six per cent, of sulphate of iron, were added 

 20 parts of sulphate of copper ; and from the solution the rhom- 

 boidal crystal was obtained. It was also obtained from a mixture 

 of f of sulphate of zinc, containing only from two to four per 

 cent, of sulphate of iron, and J- of sulphate of copper ; but on 

 increasing the proportion of this latter salt, its own crystal was" 

 produced. Pure sulphates of copper and of zinc were mixed in 

 various proportions ; but only the crystals peculiar to these salts 



* When the sulphate of iron is in small quantity, it is necessary, in order to 

 obtain the rhomboidal crystals, to concentrate the solution rapidly by heat to the 

 point or' crystallization. If left to evaporate slowly, some crystals of the sulphate 

 of copper were found nearly pure, and others containing an indeterminate mixture 

 of both salts. 



+ To ascertain the proportion of sulphate of iron in this compound, aud in the 

 crystals afterwards obtained, a given quantity was dissolved in pure water, the 

 solution was filtered, and the iron precipitated by a solution of potaifa added 

 gradually. 



