CHEMICAL SCIENCE. 271 



can separate extremely small quantities of iodine from water, it is also 

 very easy to determine these quantities by nitrate of silver or metallic 

 mercury. Thus, after washing the iodized benzine repeatedly in dis- 

 tilled water, I take it up in a pipette, and introduce it into a coined 

 tube, in which I agitate it in contact with a few drops of solution of 

 nitrate of silver or with a known quantity of mercury, until the liquid 

 is completely decolorized. In the first case, the yellow precipitate of 

 iodide of silver is washed with alcohol of 0-86 spec, grav., thrown on 

 a filter, and treated like chloride of silver which it is intended to 

 weigh. * 



In the second, the mercury is shaken with the iodized solution, and 

 the augmentation of its weight determined. These results may be 

 checked by dissolving the protiodide of mercury formed in an excess 

 of iodide of potassium. Bromine and bromides to whicn dilute nitric, 

 nitrous or muriatic acids have been added, do not communicate any 

 color to benzine ; the same is the case with chlorine and chlorides. 

 The bromine and chlorine remain dissolved in the water which serves 

 to wash the benzine ; they may be separated in the form of a white 

 precipitate by nitrate of silver. Benzine, taking up iodine without 

 possessing the property of dissolving either bromine or chlorine, ena- 

 bles us therefore to separate iodine perfectly from these two bodies, 

 and to prove in a precise manner the presence of chlorides or 

 bromides in commercial iodide of potassium. Comptes Rendus, 

 Nov., 1852. 



NEW TEST FOR NITRIC ACID, 



The want of a simple and satisfactory test for minute qauntities of 

 nitric acid and its salts has long been felt by those engaged in chemical 

 research ; for though a number of methods, more or less delicate, have 

 from time to time been proposed, most of them are objectionable, being 

 inconclusive if taken alone, inapplicable in many cases, or requiring the 

 aid of expensive alkaloids not easily procured. The test I propose, ap- 

 pears to me to be free from those objections, and accomplishes its ob- 

 ject with considerable facility ; it depends on the formation of that inter- 

 esting class of salts lately discovered by Dr. Playfair, the Nitroprussides, 

 and the beautiful and characteristic effect, produced on them by an al- 

 kaline sulphuret. I have found that the nitroprussides may be formed 

 (under certain circumstances) when only very minute quantities of 

 nitric acid or its salts are present. The method I adopt is as follows : 

 To the solid or liquid supposed to contain nitric acid, in its free or 

 combined state, add a few drops of a strong aqueous solution of ferro- 

 cyanide of potassium (yellow prussiate of potash,) then some pure 

 muriatic acid, mixing the ingredients well together both before and 

 after the addition of the acid, and gradually raise the temperature of 

 the mixture to about 160 Fahr., or in some cases it may be necessary 

 to raise it a little higher ; let it cool, and then neutralize with carbon- 

 ate of soda or potash, a slight excess of either being of no consequence. 

 Filter if there is much precipitate, and finally add to the fluid a drop or 



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