,1825.] On the Method of analyzing Sulphate of Zinc. 863 



The incidences of the faces marked a' in the figure I could not 

 obtain with great accuracy, but yet they appeared to differ 

 constantly from those of harmotome, the most obtuse being 

 nearly 123° 30', and the less obtuse 117° 30'. The substance 

 appears to cleave parallel to the planes m and t, but not in the 

 direction of the diagonal planes as harmotome, and finally the 

 hardness is much less. These differences induced me to re- 

 quest Dr. Wollaston to ascertain whether this substance could 

 be chemically considered as harmotome. The result of his exa- 

 mination was, that it contained silex, alumina, potash, and lime, 

 but not the slightest trace of barytes. 



The absence of this earth, which is an essential constituent of 

 harmotome, decides at once the propriety of separating the new 

 substance from that mineral, and to make a distinct species of 

 it. It is easy to verify the chemical difference between the two 

 substances in the following manner : if a fragment of harmotome 

 is pounded and digested for a minute or two in boiling nitric or 

 muriatic acid, and then the liquid filtered, a drop of sulphuric 

 acid put into it will give a precipitate, whilst there will not be 

 the least appearance of one, if Philhpsite be treated in the same 

 manner. I do not give the dunensions of the primitive form, 

 because the measurements are not sufficiently accurate, but it is 

 obvious that a right rectangular prism, or a right rhombic prism, 

 may be assumed as the primitive. 



Article XL 



On the Method of analyzing Sulphate of Zinc » 

 By Thomas Thomson, MD. FRS. 



In my late work entitled "An Attempt to establish the First 

 Principles of Chemistry by Experiment," I have made the 

 analysis of sulphate of zinc the foundation on which I have 

 endeavoured to rear the whole subsequent doctrine of the 

 atomic weio;ht of bodies. I was obhged to begin somewhere, 

 and the analysis of this salt appeared as simple and as decisive 

 as any other. I abstained from describing the processes which 

 I followed, because I thought them rather too tedious for a 

 work of the nature that I had projected, and because it was in 

 my power in a book intended chiefly for my own students to 

 supply verbally whatever was wanting in the practical part. I 

 find, however, that I was mistaken in the opinion which I had 

 formed of chemists, when I supposed that they would have 

 given me credit for being acquainted with the usual methods; of 

 separating the oxide of zinc from acids. For I lately received 

 a letter from a gentleman, of whose practical skill 1 entertaii a 

 high opinion, informing me that my experiments audcaloular 



