18 



Found. 



( '■ * » 



Calculated. i. ii. m. 



8ZnO, 74-529 . . . 74-759 . . . 74-869 . . . 74-337 



3C0„ 15-1441^2 , ^^'^7^125.240 ^^'^20^25-131 ^^-^^^l 25 662 

 5H:0, 10-325r^^^^ 10-165r^^^^ ll-Ill)^^^^^ 10-528 j 



When hot or cold solutions of sulphate of zinc and carbonate of soda 

 or potash are mingled; a precipitate is thrown down, which was analysed 

 by Schindler, and for which he proposed the formula 8ZnO, 300.2,6110. 

 This is also the formula which Messrs. Peterson and Veit deduced from 

 their analyses of the part taken from the centre of the mass. If we con- 

 sidered the water driven oif at 120*^ as part of the hydrated water, the 

 composition of ISTo. III. would to some extent agree with the formula — 

 to some extent only, however, for the water, which in an air-dried speci- 

 men is more likely to be in excess, is too small. But as it is only the 

 friable porous variety, which must contain most hygroscopic water, that 

 agrees with this formula, while all the compact varieties differ materially 

 from it, we could not, even if we had not positive evidence that part of 

 the water is hygroscopic, adopt the formula of Schindler. 



How are we to look upon those hydrocarbonates ? Are they com- 

 pounds of hydrated oxide of zinc and of carbonate of zinc, or are they 

 basic carbonates combined with water? If the former, Schindler' s 

 formula should be written thus :_[3 (ZnO,C02) + 5 (ZnO,HO) ] +H0 ; 

 if the latter, 8ZnO,3C02 + 6II0. In the former case the water performs 

 two functions, and one equivalent must be held with much less force 

 than the other five. It is probable that the most stable hydrate of 

 oxide of zinc, is that represented by the formula Zn0,II0 ; accordingly 

 we find that, in the majority of hydrocarbonates yet discovered, the sum 

 of the equivalents of carbonic acid and water is equal to the number of 

 equivalents of zinc. May it not be that the body examined by Schind- 

 ler was not perfectly dry ; and that its real composition was 3 (ZnO, 

 CO2) + 5 (ZnO, HO). In this case it was identical in composition with 

 the Spanish hydrocarbonate. 



"With regard to the second f jrmula of Messrs. Peterson and Yeit, 

 which assumes not merely a loss of hydrated water, but also of carbonic 

 acid, we believe that their conclusion is founded upon an erroneous 

 estimation of the carbonic acid. On looking to page 14, it will be found 

 that the amount of oxide of zinc which they found is considerably below 

 that calculated from their formula, while it is very little above that 

 deduced from our formula — indeed, their analysis of the part exposed 

 to the air for three months, so far from leading to the formula 3ZnO, 

 C03,2HO, fully confirms ours, as the following table, in which our 

 analyses are contrasted with theirs, and with the theoretical composition 

 deduced from our formula shows : — 



Calculated. I, II. III. P. & V. 



8ZnO, 74-529 . . . 74-759 . . . 74 869 . . . 74-337 . . . 74-78 



3CO2, l.'^-l^^i 15-075. 15-020. 15134 1 l^'Sl { 25-260 



6H0, 10-326^5*^^ 10-165 r^'^*^ ll-iu r^ 10-528)^5 11-45 



