5jQ4., ^^Messrs. Playfair and Joule o;i .k 



= 9^*4, which is not very far from 94*8, the volume deter- 

 mined by experiment. Bichromate of potash would consist 

 of a double atom of chromate of potash and 2 of chromic 

 acid, or 75*8 + 39*2 = 1 15-0, which agrees pretty closely with 

 the experimental determination of 115'6 j and terchromate of 

 potash, in like manner, is 1 atom of double chromate of pot^/i 

 ash with 4 of chromic acid, or 73*8 + 78*4 = 154-2, which ^a,, 

 almost exactly the same as 154*4, found in the two consecu^; 

 tive experiments, and not far distant from 153-6, the mean ot 

 the three experiments. If /.orioMi^ 



This view receives confirmation from the volume of Peli- 

 got's salt, which certainly consists of the volume of KCl, 

 when in combination, added to that of 2 atoms of chromic 

 acid, 33-0 + 39-2 = 72*2, a number very close to the experi- 

 mental result 72'6. It is quite true that we have made a;^ 

 gratuitous assumption at the outset of our explanation ; biit" 

 it is not surprising to find an unusual law prevailing in a class 

 of salts so anomalous as the chromates. When the experi-/ 

 mental numbers, and those calculated on the assumption, are^ 

 so near as we have shown them to be, there is, we think, au 

 good argument for the truth of the hypothesis. , ..^ -'^ 



° " iil JjUli t«i*bTu 'Jt •'r, t J jii ^'lOJliW to %.iliH-Vg 



■ r' .>;hi, Vi •),, iTABLE X.A. ''V OP 1r. JllOint'SJiCIXO 



Name. 



WS'/rii 





Chromic acid CrO 



Chromate of potash, doubled (2KO,2Cr03) 



Sesquichromate of potash -j ^ i p n 



Bichromate of potash . . . | ^^^^^^gcS^^"* 

 J (2KO,2Crb3) 

 I +4Cr03 



KCH-2Cr03 



Terchromate of potash 



Bichromate of chloride of 

 potassium 



O P< 



19-5 

 75-2 



94-8 

 115-6 

 154-4 



72-6 





19-6 

 75-8 



95-4 

 115-0 

 154-2 



72-2 



1^ 



o J3 



2-663 

 2-627 



2-658 

 2-638 

 2644 



2-480 





2-676 

 2-646 



2-648 

 2-624 

 2-641 

 2-466 



;)Ui 



;//o 



fJ7/ 



A singular result obtained in the examination of the anhy- 

 drous double sulphates seems to be explained by the behaviour 

 of the chromates. We found sulphate of copper and potash 

 and sulphate of magnesia and potash to affect a volume of 

 59*8 instead of 55*0, and we ascertained, by many experiments, 

 that this high number was not due to an error of observation. 

 Now, if we suppose the KO, SO3 in these salts to behave like 

 KO, CrOg in assuming one volume of ice on the double atom^ * 



119*8 ^'^ 



then 2KO, 803= 75-8 + 2M0, SO3 = 44-0 = ^—^ = 59-9,.p 



r r 



■??I.i. 



