82 Dr. Thomson on the Decomposition of Sulphate ofZinc> fyc. 



There will be deposited 



6 atoms dichromate of zinc .. =102 



By carefully concentrating the mother liquor we 

 obtain 1st, 5 atoms bichromate of potash... s 95 



2nd, 4 atoms potash-sulphate of zinc = 85 



3rd, 6 atoms sulphate of potash = 66 



4th, 1 atom bisulphate of potash. ... = 16 



Total 364 



All these salts are conceived to be anhydrous, merely to sim- 

 plify the numbers. 



The practical chemist will easily understand how I pro- 

 ceeded. 1 evaporated the liquid as carefully as possible, pick- 

 ing out the crystals as they formed, and examining them. I 

 easily recognized bichromate of potash, potash-sulphate of 

 zinc, and sulphate of potash, by their forms. I did not perceive 

 any crystals of bisulphate of potash, I merely inferred the for- 

 mation of this salt from the impossibility of accounting in any 

 other way for the formation of the other four salts from the 

 atoms which I had mixed, unless the formation of that salt 

 also be admitted. The reader will not suppose that I suc- 

 ceeded in separating the whole of these four salts from each 

 other, I merely endeavoured to determine the nature of all 

 the salts formed. The rest was the result of an obvious cal- 

 culation. 



From Mr. Stokes's experiments it would appear that similar 

 salts are formed when sulphate of nickel or sulphate of copper 

 is mixed with chromate of potash in the atomic proportions. 

 This I have not hitherto had occasion to investigate. But it 

 will probably turn out that my chromate of nickel and chro- 

 mate of copper are in fact, dichromates. This I shall endea- 

 vour to ascertain os soon as I have leisure. 



I am, &c. 



Dec. 14, 1827. Thomas Thomson. 



XIV. On the Measurement by Trigonometry of the Heights of 

 the principal Hills in the Vicinity of Dent, Halves, and Sed- 

 bergh, in Yorkshire. By John Nixon, Esq.* 



HPHREE years ago I commenced, and in the course of the 

 -■- present summer I succeeded in completing, the trigono- 

 metrical measurement of the heights of a group of hills of the 

 Penine chain. Different observers have generally furnished 

 from similar operations results so extremely discordant, that 



* Communicated by the Author. 



it 



