6^ .^t.T^VMessrd. Playfeir cmd Joule on 



isbynomeans UQCommon, aud is /again seen in the subchrdfi 

 mates of lead. Chromate of lead has a volume sensibly the 

 multiple^f^^S. ~ ^:- w • 



-m 33f» MM imri ^i' experiment. By calculation. 



Chromate of lead 29-0 ...5-653 ... 9*8 x 3=:29-4 ... 5-577 

 Boullay gives the specific gravity of oxide of lead as 9*5, 

 which indicates the volume 11*7, a number not far from 11, 

 which we take as the unit volume. Subchromate of lead con- 

 sists of one equivalent of the neutral chromate united to one 

 of oxide of lead, but the three volumes of ice in the former have 

 changed in the subsalt to 11 x 3, and the same is the case in 

 the mineral raelanchroit, which contains two equivalents of 

 chromate of lead united to one of oxide of lead. 



J Subchromate of lead, PbO, Cr03+PbO = 44 or 11 x 4 

 Melauchroit, 2 (PbO, CrOg) + PbO ni 76^3 or 11 x 7 

 In these salts we clearly see that oxide of lead takes up 

 the volume and plays the part of an atom of water, although'' 

 we are ignorant of their hydrated types. The same function^ 

 of an oxide is seen in turpeth mineral, in Mhich the 2HgOf 

 attached to HgO, SO3, assumes the volume of two atoms of 

 water, 22 + 22 = 44. There can be little doubt from the pre- 

 vious examples of the equivalency of CuO, ZnO, BiO, HgOp 

 and PbO, not only to each other but also to \vater ; and this 

 will be still more strongly seen by placing the volumes of these 

 and other anhydrous magnesian sulphates along with the vo- 

 lume of sulphate of water itself, as deduced from bisulphate 

 of potash. 



Sulphate of Water, vol. by experiment 22*0 

 Zinc ... 21-8 



Copper ... 22*0 •'^"t 



Iron ... 24*0 



Cobalt ... 22-0 



Mercury ... 23*1 > s* 



The only cases in which there is an appreciable difFerencfe!'* 

 from sulphate of water are those of sulphates of iron and*^' 

 mercury, neither of which salts can be obtaijie^ wLthout diflEi?'^ 

 culty perfectly pure in an anhydrous state. " "^ " ^ ^^^ 

 But if the equivalency of the magnesian metals to eacft^ 

 other and to hydrogen be left in any doubt by the preceding* 

 table, this doubt would be entirely removed by a consideration 

 of the magnesian chlorides. The strongest muriatic acid ob- 

 tained has, according to Thomson, a specific gravity of 1 '203^^11 

 and contains 40*66 per cent, of dry muriatic acid ; which is 

 equal to 5*91, obviously six atoms of water to one of muriatic 



