On the Proportion of Water in the Magnesian Sulphates. 289 



for different things. For example, the original English sense 

 of the word square applies to an angle, not a figure; a right 

 angle is a square corner; and to this day the carpenter's right 

 angle is called a square. But I could name half-a-dozen 

 writers of the end of the sixteenth century who use the two 

 spellings square and squire* the former in the modern sense, 

 the latter for the carpenter's instrument. 



XLVII. Reply to the Observations of M. Pierre, on the Pro- 

 portion of Water in the Magnesian Sulphates and Double 

 Sulphates. By Thomas Graham, Esq., F.R.S.* 



IN a late number of the Annates de Chimie, a paper by M. 

 Isidore Pierre appears, On the Double Salts formed by 

 the Oxides of the Magnesian Group, of which an abstract is 

 also given in the March Number of the Philosophical Maga- 

 zine, containing statements which demand some remark from 

 myself. It presents new analyses of the sulphate of magne- 

 sia and potash, and other double sulphates of the same type, 

 from which the author infers that these well-known double 

 salts possess seven atoms of water crystallization, and not six 

 atoms, as resulted from my own analyses and the analyses of 

 all other chemists who have of late years examined these salts. 

 The double salts in question are thus made by M. Pierre to 

 have the same proportion of water as sulphate of magnesia 

 itself; while the latter salt, also, is not found to retain its 

 seventh atom of water more strongly than the other six, but 

 to become anhydrous at 212°, or a few degrees above that 

 temperature, in a current of dry air. The author then infers 

 that his results are subversive of the theory which was ori- 

 ginally published by myself, of the constitution of the mag- 

 nesian sulphates, and to which I still adhere, namely that 

 they contain an atom of water strongly attached and not easily- 

 expelled by heat, but readily replaced by an alkaline sulphate, 

 with formation of a double salt. 



Although confident of the accuracy of the analyses thus im- 

 pugned, I considered it due to M. Pierre, who, although a 

 young chemist, has afforded every evidence of habitual care 

 and accuracy in another experimental inquiry of importance, 

 to repeat my experiments. 



Of the double sulphate of zinc and potash, 31*46 grains by- 

 drying at 212° for several days, lost 7*75 grains of water ; and 

 by fusion at a heat verging on redness, 0'08 grain of water 

 additional, making the whole loss 7*83 grains. Hence the 

 composition of the salt with reference to water is as follows : 

 * Communicated by the Author. 



Phil. Mag. S. 3. Vol. 28. No. 1 87. April 1846. X 



