480 H. Reinsch on the action of Metallic Copper on Solutions 



1_ 



n 



(T+l)- 2 



, a . . i * i> il.2.3...« 2 1 



deficiency is greater than — — — — — — -, . p =£, 



1.2.3...W 2 1 



and less than 



1.3.5...(2w+l)' P„ ' rj^±i' 



The number n is arbitrary, but had better be taken large 

 when the number t is small. 



If we take n — 10 when t = 1, we find by this rule log 2 



5612726 4 — 

 = on ^/n° i which converted to a decimal is necessarily ac- 



oVi)t J *5o * 



curate to the 15th place inclusive, which is known by the 

 above limits. 



By the application of this and similar methods, a mere 

 arithmetician will be able to calculate logarithms, accurate to 

 any extent, and to their last decimal figure. 



Robert Murphy. 



P.S. In my paper contained in the last Number, p. 369, 

 for " a is a primitive radix," read a is the next superior pri- 

 mitive radix. The following numbers are verified instances 

 of the general formula in that paper, viz. (3 n 2 4-2)5, 29, 149; 

 (5w 2 + 3)23,83;(15« 2 + 13), 73; (20 rc 2 -f 17) 37; (21 w 2 +19), 

 103, and several others, and I have not met with an excep- 

 tional case. 



M 



LXXII. On the Action of Metallic Copper on Solutions of cer- 

 tain Metals, particularly with reference to the detection of 

 Arsenic. By H. Reinsch*. 



REINSCH was induced to enter into the examination 

 • of the action of copper on certain metallic solutions, and 

 its application as a test for arsenic, from the circumstance of 

 having obtained a precipitate of metallic arsenic upon a piece 

 of copper immersed in commercial hydrochloric acid. 



This action of metallic copper he considered the more im- 

 portant, as by that means he hoped to be able to devise a 

 simpler method of detecting arsenic, and also of separating it 

 from solutions, which might be less liable to objection than 

 that by Marsh's apparatus, the uncertainty of which has been 

 lately pointed out by the experiments of MM. Danger and 

 Flandin. 



The process is founded upon the same principle as that 



* The above is an abstract from a paper in Erdmann's Journal fur Prak- 

 tische Chemie, No. 19, 1841. 



