Proceedings of tue Polytechnic Association. 759 



The comparatire economy of this process we are iiiialjle to give, but 

 any plan for. cheapening the production of the most important mine- 

 ral aeicl will excite great interest among manufacturing chemists. 



Test foe I^aputualine. 

 Yohl states that when naphthaline is treated with concentrated 

 nitric acid, and the mixture is diluted with water, a precipitate is 

 produced, which after being washed first with water anJd then with 

 diluted alcohol (three-fourths water), may be placed in a watch-glass 

 with a few drops of a solution of hydrate of potassium and pf 

 sulphide of potassium and evaporated to dryness on a water bath. 

 On moistening the residue with alcohol, a magnificent red violet 

 color is immediately developed. 



Measukixg Telescope. 

 The ordnance select committee of the war department of Great 

 Britain have approved of the telescope patented by Messrs. Elliot 

 Brothers, London, which enables the distance of either infaatry or 

 cavalry to be computed 'instantaneously. The distance is obtained 

 by means of two wires moved by a disc, on which are divisions 

 showing the remoteness of the object, which is in ratio to th6 prox- 

 imity of the two v\'ires between which it is seen. The motion of the 

 wires is produced by a double eccentric mo^■iug round the smaller 

 tube of the telescope. 



Cerium. 



The late Dr. Charles AYolf, of Cincinnati, Ohio, wliile in the 

 laboratory of Buusen in Heidelburg, Germany, made an elaborate 

 investigation on the equivalent of cerium. The papers containing 

 an account of his experiments and calculations have been translated 

 for The Arnerican Journal of Science and Arts by Mr. F. A. Genth, 

 of Philadelphia. The result of the investigation is the number 

 45.604 (estimating oxygen at eight) as the equivalent of the purest 

 cerium. 



Obseevatio:?^ of IS^ebula. 



Father Socehi, of Home, in a communication to the Royal Astro- 

 nomical Society, London, "On tlic great nebula of Orion,"' states 

 that the nebula is seen nmch better in moonlight than on dark nights. 

 This surprising effect ho accounted for upon the optical principle,, 

 that the diiierence of two lights is more easily' appreciated wlien they 

 are "weak than when they are strong. 



