rftf On tM Piiriflcaitoh of NicUl. 



lacious indications of strength without its beitlg pftrc^it^ed 

 by the owner of them. The fact i;;, however, that akhough, 

 for certain purposes, where metalHc instruments cannot be 

 used on account of their being liable to corrosion (as in the 

 case of the mineral acids) we are obliged to employ glass^ 

 yet they are by no means capable of being rendered so ac- 

 curate as those which are made of metal. The proportiort 

 of the bulb to the stem, and the consequent extent of thd 

 graduations, are, of course, within certain limits, malicrS 

 of mere chance ; and they are, therefore, not the subject of 

 calculation. Every such instrument can only be graduated 

 by direct experiment : and to those who \\ould contend for 

 the. eligibility of such a method, where the other can ht 

 Used, we can only say, that they have not sufficiently con- 

 sidered the subject. The metallic stems and bulbs, on the 

 other hand, are by the tools employed for tliese purposes 

 capable of being reduced so accurately to the required biilk, 

 that the error in any point of the scale on this account will 

 fiot amount to one-tenth of an unit in the specific gravity. 

 Nor is it true that it is easily possible for the effect of such 

 &n accidetit to pass unnoticed by any one who ought to be 

 entrusted with the use of an instrument at all. The least 

 want of proper convexity in the bulb strikes the eye in aA 

 instant, even before its effect would be such as to be per- 

 fceptible in the indication on the stem ; and if it werfe 

 not so, the simple operation of immerging the hydronietel-, 

 loaded with its proper weight in distilled Or rain watei- at 

 CO**, would at once detect such a circumstance, so that no 

 J)robable inconvenience can ever result from such a cause. 

 £ro be continued.] 



LVII. On the Purificaiion of Nickel, with some Re?narks on 

 the Solutions of metallic Oxides in Ammonia, ^c. By 

 Mr. R. Phillips, Member of the Askcsian and British 

 Mineralogical Societies *. 



JcXLTHOUGH nickel has been discovered more than a cen- 

 tury, yet its existence as a peculiar metal has not been so 

 well established but that several chemists, even of late years, 

 have entertained considerable doubt on the subject. 71iis 

 Ms probably been occasioned by the difficulty in separating - 

 It from t^e metals with which it is usually mixed. Of thes« 

 'copper and cobalt, and niore particularly the latter, strongly 



* Comiatifticatcd by the Author; 



resemble 



