Chemical Science, 343 



of colour at the same heat, and it was uniformly found, after 

 several trials, that the depth of the colour depended on the fine- 

 ness of grinding. Nitre destroyed the colour in the fire. 



Specimens were sent to the editor, according to whom the pul- 

 verised portion, exposed to a low red heat, was of a peach blos- 

 som colour ; another portion, exposed to a higher temperature, 

 pale bluish lilac ; a third portion, exposed to a moderate white 

 heat, was a slightly greenish white enamel ; and a fourth portion, 

 mixed and heated with one fifth nitre, was like the second of the 

 above.— ^ww. Phil N. S. ix. 432. 



12. On the means of Testing for Iodine. By M. Balard. — Not- 

 withstanding the delicacy of the test for the presence of iodine af- 

 forded by the use of starch, its value is considerably diminished by 

 the facility with which various substances interfere with its action ; 

 and this is especially the case when any of those bodies which, 

 either alone or with water, yield hydrogen are present : the iodine 

 becomes hydroidic acid, and the blue colour either disappears, or is 

 not formed. Sulphurous acid and sulphuretted hydrogen, substances 

 almost constantly produced by the incineration of organized 

 bodies which contain earthy or alkaline sulphates, are especially 

 capable of producing this effect. 



Among the various means of obviating this inconvenience is the 

 use of chlorine, and during his experiments on the products of the 

 Mediterranean, M, Balard has been led to apply it in the following 

 manner: — After having mixed the liquid containing the iodine 

 with the starch and the sulphuric acid, a small quantity of aque- 

 ous solution of chlorine is to be added, which from its lightness 

 may be made not to mix with the mixture, but float on the surface. 

 At the place, however, where they touch, a blue zone will be per- 

 ceived, which, however feeble it may be, is readily seen by con- 

 trast with the neighbouring limpid liquids ; if a part of the mixture 

 be slightly agitated, the blue colour will be developed where 

 the two solutions are in contact ; but if the whole be mixed, it 

 will entirely disappear, if the chlorine be in excess. 



By means of this test thus applied, M. Balard has found iodine 

 where it could not before be observed, as in the various marine 

 moUusca, testaceous or not, such as the doris, venus, oysters ^ &c., 

 many polypi and marine vegetables, the gorgonia, the zostera 

 marina, &c., and especially in the mother water of the salt pans 

 fed by the Mediterranean. The small quantity of iodine which is 

 found in sea-water, he believes, from the mode of action of the 

 test, to exist as a hydriodate. 



M. Balard expresses his conviction that a process of this kind 

 will save chemists the trouble of many fruitless trials, and lead to 

 decided and positive results, where otherwise none would be 

 obtained. — Ann. de Chimie, xxviii. 179. 



