Chemical Science. 173 



7. PREPARATION OF PHOSPHURET OP LIME. (Dr. Coxe.) 



1 employ two Hessian crucibles, some of the inner members of 

 a nest. The larger of the two has a hole bored through its 

 bottom, and a test tube of a suitable size luted in with clay. The 

 phosphorus is put into the test tube, the top of which is loosely 

 covered with a piece of broken crucible to prevent the small pieces 

 of quicklime from running down into it. The lime is then put in 

 so as to fill this crucible and partly fill the upper smaller one, 

 which serves as a cover to it, and is luted on with some fine clay 

 a little moistened. The cover has also a small hole in its top to 

 afford an outlet for the air, or volatilised phosphorus, if there should 

 be any occasion for it. The whole is now placed upon the grate of 

 a furnace, with the test tube projecting through and appearing 

 below, and a charcoal fire kindled around it. The phosphorus may 

 be kept cool if it should be ' thought necessary, by making the tube 

 dip into the water, contained in a tin cup attached to the end of a 

 stick. When the crucibles and their contents are thoroughly red 

 hot, a chafing dish is substituted for the tin cup, and the phos- 

 phorus rising in vapour produces the desired change. The phos- 

 phuret should be preserved in a sealed vial. The same crucibles 

 may be used a number of times*. 



8. IODIDE OF POTASSIUM A GOOD TEST FOR ARSENIC CURIOUS 

 COMPOUND PRODUCED. 



Professor Emmett of Virginia has recommended the iodide of potas- 

 sium, or iodine alone occasionally, as a useful test for white arsenic. 

 He found that when the iodide was added to a solution containing 

 only 2.8 per cent, of arsenious acid, or 1.8 per cent, of arsenite 

 of potassa, or when iodine alone was added to a solution containing 

 2.8 per cent, of arsenite of potassa, an immediate precipitation took 

 place. If the precipitation be performed with drops upon a glass 

 plate, then -jj^dth of a grain of arsenic is sufficient for the pur- 

 pose; the precipitate, when gradually formed, is white, adheres with 

 great tenacity to the glass plate, and then may be thoroughly washed, 

 and will present the following characters. Concentrated nitric acid 

 changes the white colour to a dark brown, purple, or even black, 

 from free iodine ; and starch added at the same time, becomes deep 

 blue. Strong hot sulphuric acid does the same ; when cold, it 

 merely produces a bright yellow, the latter effect is produced by 

 strong muriatic acid. Metallic salts are not likely to cause errors 

 in the use of this test, because, if originally present, they are sepa- 

 rated by the carbonated alkali used to dissolve the arsenious acid. 

 The presence of coffee, tea, milk, and other liquids, does not seem 

 materially to retard the precipitation. 



The substance thus formed appears to be a curious compound. 

 It resembles arsenious acid in solubility and precipitation ; thus, 



* Sillimaa's Journal; xvii. 349. 



