Chemical Science. 415 



having- the power of decrepitating in water like that described. — 

 Revue Ency. xlvi. 245. ' « ^f ^ x>3xoqquv 



8. lodates of Potassa. Chloriodate of Potassa^ 8fc. SeruWasi^ 

 Biniodate of Potassa. When an alcoholic solution of chloride' 6f 

 iodine is mixed with an alcoholic solution of potassa, an acid iodate 

 of potassa is precipitated. This salt may be obtained more abun- 

 dantly, by adding to an aqueous solution of chloride of iodine a pure 

 solution of carbonated or caustic potassa, not quite sufficient to 

 saturate it; heat is evolved, but, on cooling, a crystalline precipitate 

 is formed, which consists of definite proportions of chloride of potas- 

 sium and acid iodate of potassa; chloro-iodate of potassa. This 

 deposit being separated, is to be dissolved, filtered, and placed in a 

 warm air-chamber at 77° F. In twenty-four hours, if the solution 

 is sufficiently dilute, very regular and pure crystals of the acid 

 iodate of potassa will be formed ; they are right rhombic prisms, 

 terminated by two diedral summits: 1 part dissolves in 75 of water, 

 at 59° F. The liquid is then to be quite neutralized, for the pur- 

 pose of procuring the neutral iodate in -the ordinary way. 



Being carefully heated until all the water was dissipated, which 

 happens just as violet vapours appear, further heat then evolves 

 oxygen and iodine, and leaves iodideof potassium; 5 parts gave 2.1 

 parts of iodide of potassium, and then, by the usual means, gave 3 of 

 iodide of silver. By continuing the analysis, it was ultimately 

 proved that this substance was a biniodate of potassa, consisting of 

 1 atom potassa, or 22.246, and 2 atoms of iodic acid, 155,508. The 

 truth of Gay Lqssac's analysis of the neutral iodate was also proved, 

 namely, 22.246 base, and 77.754 acid. 



Tri-iodate of Potassa. — When neutral iodate of potassa is acted 

 upon by sulphuric, nitric, phosphoric, muriatic, or silicated fluoric 

 acid, a part of the base is removed, and an acid iodate results, con- 

 taining thrice the quantity of acid as the neutral salt. It is crystal- 

 line, and generally rhomboidal in form. The best process is to heat 

 a solution of the neutral iodate of potassa with great excess of sul- 

 phuric acid; to filter the solution, which should not be concen- 

 trated, and leave it to evaporate spontaneously, or in a warm air- 

 chamber at 77° F. Regular rhomboidal crystals are readily formed, 

 which are transparent and very pure tri-iodate of potassa. This 

 salt is distinguished from the bin-iodate by its property of gradually 

 becoming red ; 1 part dissolves in 25 of water, at 59° F, This salt 

 is readily formed by adding potash to great excess of iodic acid, and 

 crystallizing the result. By analysis the composition was determined 

 to b(9,, . Potassa . . 8.76 . 1 atom. 



Iodic acid . . 91.29 . 3 atoms. 



This salt, dissolved and crystallized, passes into bin-iodate, but if 

 tlie solution be concentrated after the first crop of bin-iodate, then 

 crystals of the tri-iodate appear. 



M. Servillas then endeavoured to form those salts which have 

 been said to exist, containing a double acid, the iodic acid being 



2E2 



