CHEMICAL SCIENCE. 179 



and mixed with varnish to give it a body and consistency. The red 

 oxide of zinc also makes an excellent, quickly drying red paint. By 

 adding lamp-black, Prussian blue, and other colors, any shade of paint 

 may be readily obtained, free from the disadvantages of lead. 



OCCURRENCE OF ARSENIC IN IRON PYRITES. 



BREITHAUPT has examined a vast number of iron pyrites for arsenic, 

 which metal he finds to be most extensively diffused, forming in gen- 

 eral from to 1 per cent. It is probable that all the iron pyrites upon 

 heavy spar and fluor spar contain arsenic. Pogg. Annalen, Vol. 

 LXXVII. p. HI. 



ARTIFICIAL CRYSTALS OF SESQUIOXIDE OF CHROMIUM. 



AT the meeting of the American Association, at New Haven, Mr. 

 Blake called the attention of the members to some artificial crystals of 

 sesquioxide of chromium, formed between the cracks of the floor of a 

 furnace used for the production of chromate of potassa from the min- 

 eral chromate of iron. The furnace had been in operation for more 

 than a year, and kept at a temperature above redness. The crystals 

 have the hardness of sapphire, and resemble crystals of specular iron. 

 Their lustre is metallic, color black. Wohler obtained crystals of 

 sesquioxide of chromium by passing the vapor of chlorochromic acid 

 through a tube heated to redness. Silliman's Journal, Nov. 



NEW METHOD OF DETERMINING URANIUM IN ITS ORES. 



A WEIGHED quantity of the ore is dissolved in nitric acid, filtered 

 from the residuum, and then saturated with an excess of carbonate of 

 potash, whereby the uranium remains in solution as neutral uranate 

 of potash, with arsenic and sulphuric acids, when these are present. 

 All the other metals in combination are precipitated as carbonates and 

 separated by filtering. The soluble neutral uranate of potash is then 

 boiled in a gilt silver vessel, whereby acid uranate of potash is formed, 

 which is insoluble in water, is easily washed, and from which the 

 quantity of uranium can easily be determined. Journal of Franklin 

 Institute, June. 



CHEMICAL CONSTITUENTS OF IRON. 



IN the evidence given before the commissioners appointed to inquire 

 into the application of iron to railway structures, as reported in the 

 Civil Engineer and Architect's Journal for February, we find some in- 

 teresting facts. The strength of cast-iron depends upon its freedom 

 from impurities and upon the proportion of carbon it contains, the 

 strongest containing about three per cent., or, according to Mr. C. 

 May, when the carbon is in the smallest proportion that produces 

 fluidity, a larger proportion tends to make the iron soft and weak, and 

 a smaller hard and brittle. Mr. Glynn says that the strongest iron 



