408 MisceUaiieous Intelligence. 



The equivalent number for sulphate of magnesia is 24.7129- 

 For the dry sulphate, 74.8294, and this quantity combines 

 ■when in the crystalline form, with 79.236 of water, or seven 

 proportions. — Annalesde Chim. xiii. p. 308. 



13. Test for Copper and Iron. — The ferro-cyanate of potash has 

 long been used as a test for copper and iron in solution, and it is 

 hardly possible to imagine any thing more sensible than its in- 

 dications. M. Brandenburgh, however, recommends, as superior 

 to it, the ferro-cyanate of ammonia (prussiate of ammonia and 

 iron). It is easily prepared by pouring ammonia on to Prussian 

 blue in a phial, which must be closely stopped. About six of 

 the former to one of the latter may be used at first ; and if, in the 

 course of three or four days, the whole of the sediment has be- 

 come brown, more of the Prussian blue is to be added, until it 

 ceases to change colour. The solution is then filtered, that 

 which remains adhering at first to the residuum, being passed 

 through by washing, and is then preserved for use. It should 

 be of a fine yellow colour. 



14. Properties of Native Naphtha. — Dr. Thomson has lately 

 ascertained tlie properties of native naphtha. The specimen on 

 which he worked came from Persia, and was very pure. It was 

 perfectly colourless, and had the taste and smell of the naphtha 

 which is made in this country from coal. Its specific gravity 

 was .753. The lowest specific gravity observed of naphtha made 

 in this country was .817. It was not very volatile ; it boiled 

 at 320°; and if the boiling were continued, the temperature 

 would rise up to 338°, and in a silver vessel even to 352°. 

 This gradual rise of temperature Dr. Thomson is inclined to 

 attribute to a partial decomposition of the naphtha by the heat. 



From an attempt to analyze it, by passing one grain of it 

 through heated peroxide of copper, the following composition 

 was deduced : — 



1 3 atoms carbon 9-75 



14 atoms hydrogen. . . . 1.75 



A deficiency of 3 per cent., however, remains, which Dr. 

 Thomson was inclined to think is nitrogen. 



