336 



position of every point might be determined with sufficient exactness 

 for every practical purpose. 



The time required for such an examination is estimated to be about 

 ninety-eight hours, and the labour, no doubt, is very considerable ; 

 but when the errors thus ascertained have been duly noted in a table, 

 Mr. Lax considers the utmost pains that can be bestowed upon any 

 instrument to be amply compensated by the confidence given to 

 every subsequent observation by means of it. 



It is also proposed occasionally to obviate the effects of unequal 

 expansion in any particular observation, by comparing the arc by 

 which any angle has been measured with several succeeding equal 

 arcs, until the multiple exceeds the whole circumference, and thereby 

 includes the opposite errors, which arise from this cause in different 

 parts of a circle, and correct each other. 



On the Identity of Columbium and Tantalum. By William Hyde Wol- 

 laston, M.D. Sec. R.S. Read June 8, 1809. [Phil. Trans. 1809, 

 p. 246.] 



The author having received specimens of the Swedish mineral tan- 

 talite, containing the metal called Tantalium, by Mr. Ekeberg, was 

 desirous of ascertaining whether that metal might not be the same 

 as columbium, which had been discovered a short time before by 

 Mr. Hatchett ; and for that purpose he procured some oxide of co- 

 lumbium from Mr. Hatchett, and also a fragment of the mineral in 

 the British Museum, originally analysed by Mr. Hatchett. 



He describes the external resemblance to be such, that one might 

 be taken for the other ; but observes, that the columbite is rather 

 more brittle than tantalite. 



By analysis, also, he finds them to consist of the same three in- 

 gredients ; namely, a white oxide, iron, and manganese. 



To separate these substances, the mineral is powdered and fused 

 with carbonate of potash and a small proportion of borax. The iron 

 and manganese may then be dissolved, along with the salts employed, 

 by muriatic acid, and the oxide of columbium or tantalium remains 

 as a white powder for further trial of its properties. 



Five grains of columbite being thus treated, left four grains of 

 white oxide ; and the solution yielded three fourths of a grain of 

 iron, and one fourth of a grain of manganese. 



Five grains of tantalite, by the same treatment, left four grains and 

 a quarter of oxide, half a grain of iron, and two tenths of a grain of 

 manganese. 



The white oxides obtained from each of these minerals appear to 

 the author to have precisely the same properties. 



They are each soluble by means of about eight parts of potash. 



They are both very imperfectly soluble by means of soda. 



They are both insoluble in nitric, muriatic, succinic, and acetic 

 acids. 



They are both very sparingly soluble in strong sulphuric acid 



