CHEMISTRY. 411 



a different coiupositiou. The dark salts are in general less soluble; 

 their density is lower and tliey often contain a smaller number of mole- 

 cules of crystalline water. The difference between the two classes of 

 salts does not depend on the water of crystallization, because both dark 

 and yellow anhj'drous salts have been obtained, and because there exist 

 both yellow and dark salts containing the same number of molecules of 

 crystalline water. 



The salts of platosooxalic acid are in general sparingly soluble in cold 

 dilute acids ; they are insoluble in alcohol. In hot water some of them 

 dissolve readily ; others are sparingly soluble. Most of them contain 

 crystalline water, which they lose in part or entirely at 100°. They 

 bear the temperature of 110^ to 115^ (though the ammonium salt is 

 decomposed at 100*^) ; but a little above this temperature they begin to 

 decompose. If suddenly heated they are decomposed with detonation. 



Platosooxalic acid, Pt04O8H2+2H2O, the preparation of which has 

 been described above, giv^es, when its solution has been evaporated in 

 a vacuum, a red crystalline mass of a metallic luster. It dissolves 

 readily in water with an indigo-blue color, but this color changes to 

 yellow on heating or diluting with water. Yet the blue color returns on 

 cooling or on concentration. 



There are two potassium salts, a brown one forming copper-colored 

 needles of specific gravity 3.01, and a yellow one in hexagonal prisms 

 of specific gravity 3.03. Both contain the same number of molecules 

 of crystalline water. With the ammonium salts the case is similar. 

 The dark sodium salt forms slender needles containing 4 molecules of 

 crystalline water, whilst the yellow salt forms prisms with 5 molecules 

 of crystalline water. There are three isomeric calcium salts : the brown 

 one, with G^H20j the /^-yellow salt, with dHzO, losing one molecule water 

 at 100°; and the ;/-yellow salt, with 8H2O, losing at IOO05H2O. There 

 are also three strontium salts : a, dark, contains 3JH2O and loses ^H20 

 at 100°; /?, also dark, contains 6JH2O, and loses 3H2Oatl00O; and 

 y, yellow, contains only 3 molecules of crystalline water and undergoes 

 no change at 100°. 



These researches were made in the laboratory of Prof. P. T. 016 ve. 

 (Bull. Soc. Chim., 1886, 188.) 



lodoaldekyde is obtained by P. Chautard by acting on an aqueous 

 solution of aldehyde with a mixture of iodic acid and iodine. 



5(C2H40) + 41 + IO3H = 5(C2H3lO) + SH^O 



lodoaldehyde forms an oily, volatile, non-inflammable, colorless, 

 limpid liquid, blackening rapidly on exposure to light. It decomposes 

 at 80° C, but in solution may be heated to high temperatures without 

 change. It acts as a strong caustic, attacking eyes and respiratory 

 organs. Its density is 2.14 at 20°. It is soluble in all proportions in 

 alcohol, ether, benzene, chloroform, etc. It combines readily with ani- 

 line and other ammonia derivatives. (Comptes Rendus, cii, 118.) 



