RECENT ADVANCES IN SCIENCE 633 



by using equimolecular proportions of the two reacting salts 

 dissolved in their own weight of water, and heating at 150 

 in a closed vessel. The calcium sulphate so obtained is a sandy 

 crystalline mass readily susceptible of washing by decantation 

 with hot water, and from which practically the whole of the 

 ammonium nitrate can be obtained, free from calcium sulphate, 

 in two washings. 



Of more scientific than industrial interest is the method of 

 preparation of chlorites discovered by Bruni and Levi (Gazzetta, 

 191 5, 45, 161). Pure barium chlorite can be obtained by the 

 action of chlorine dioxide and carbon dioxide which have been 

 freed from chlorine, on barium peroxide suspended in hydrogen 

 peroxide solution. The sodium salt can be prepared from the 

 barium salt by double decomposition with sodium sulphate, 

 and a red basic mercuric salt 3Hg(C10 2 )2-HgO is obtained 

 when mercuric nitrate is used. Other insoluble salts are 

 obtained in a similar manner, but the ammonium and hydroxyl- 

 amine bases are exceptions. The mercuric salt is explosive 

 in the d^ state and with concentrated sulphuric acid all the 

 solid chlorites deflagrate more energetically than the corre- 

 sponding chlorates. The soluble salts do not give a precipitate 

 with mercuric chloride, but the red precipitate is formed when 

 mercuric nitrate is added to a neutral and not too dilute solution . 

 The mercurous salt is yellow and unstable and rapidly oxidises, 

 to the red salt in the air. 



Analytical. — A rapid and accurate method of estimating 

 chloride and bromide in presence of each other has been devised 

 by Meyer {Chem. Zeit. 191 5, 39, 708), which ought in future to 

 find a place in analytical text-books. A known volume of the 

 mixed halide solution is titrated with N/10 silver nitrate 

 solution. An equal volume of the solution is completely pre- 

 cipitated with silver nitrate solution and the mixed AgCl and 

 AgBr precipitate is collected in a Gooch crucible, washed, 

 dried, and weighed. The titration gives the weight of silver 

 in this precipitate and the difference of the two weights gives 

 the weight of chlorine and bromine together. From this latter 

 the amount of each can easily be determined by a simple 

 calculation. 



Constitution. — A lengthy paper by Weitz {Ann. der Chem. 

 1915, 410, 17) on the nitrogen compounds of gold contains 

 some data which is of importance from the point of view 



