Chemistry and Physics. 53 



flask of 180 to 200 c. c. capacity, having two tubulures, and 

 placed in a vessel of cold water. In it are placed 25 grams of pure 

 zinc, on which is poured sulphuric acid diluted with five parts of 

 water. The disengaged gas passes through cotton and then 

 throujrh a tared glass tube heated to redness by charcoal for a 

 ■^ of 20 to 25 cm. The air being expelled, the arsenic, mixed 

 nore dilute sulphuric acid is poured into the apparatus in 

 small portions, an hour being required for the introduction of 5 

 mous oxide. The 



!i;r™; 



is kept 

 ilphate hinders, platinum chloride facilitates the separ; 



hours longer, by which time all the arsenic has been ( 

 Copper sulphate hinders, plal 



tion of the arsenic from the solution. After the evolution of gai 

 ceases, the tube containing the annulus of arsenic is weighed 

 again and the amount of arsenic determined. The results are 

 very accurate. In two experiments, in which 5 milligrams arsen- 

 ous oxide were mixed with 100 grams muscular tissue, the rings 

 weighed 3-72 and 3-67 milligrams respectively ; the theoretical 

 quantity being 3-79 milligrams. In a third, 2 A milligrams arsen- 

 ous oxide were mixed with 100 grams blood ; the annulus weighed 

 1-78 milligrams, the calculated weight being 1-88 milligrams. In 

 2-1 grams of the brain of a rabbit, fed for 15 days with doses of 

 arsenous oxide gradually increasing from 5 to 50 milligrams, the 

 arsenic recovered was sufficient to give a brilliant ring nearly a 

 centimeter long. A vigorous dog was fed with gradually increas- 

 ing doses of arsenous oxide, from 4 to 80 milligrams, for a month. 

 100 grams of the liver yielded 5-3 milligrams, and 100 grams of 

 muscle yielded 0-27 milligram of metallic arsenic— J5m//. Soc. 

 Ch., II, xxiv, 250, Oct., 1875. G. f. b. 



4. Formation of Nitritea by Bacteria. -The presence of nitrites 

 in spring waters, which has usually been ascribed to the oxida- 

 tion of ammonia therein, is now stated by Meisel to be pro- 

 duced by the reduction of nitrates by the agency of bacteria. In 

 proof of this, he shows : that such water which contained bac- 

 teria and nitrates, but neither ammonia nor nitrites, gave, after 

 standing four days, the reactions of nitrous acid ; that antiseptics 

 such as salicylic acid, phenol, benzoic acid, alum, and much salt 

 even, prevent or hinder the production of nitrites ; that aque- 

 duct-water containing pure nitrates, which alone does not show 

 the production of nitrites even in presence of bacteria, has this 

 change effected upon the addition of glucose, gum, dextrin cellu- 

 lose, starch, etc., in the course of from 2 to 14 days; that freshly 

 distdled water, boiled with glucose and niter, shows no nitrites 



ninates reduce nitrates to nitrites. The de- 

 uii of cellulose by bacteria in presence of nitrates proves 

 • is not only direct food for plants, but that it also per- 

 its oxygen an important function in the soil. The au- 

 'ves that these facts have important bearings in aoricul- 

 in medicine.-i?er. jBer?. Chem. Ges.,\\\\, 1214, Oct.'' 1875 



