The Rediidion of Osmic Acid hy Lipoids. 19 



contained some organic matter used in the reduction, and that its 

 properties were modified by this substance. In later experiments 

 we hope to be able to examine more definitely the properties of 

 osmium dioxide, and of the black substance used in this experi- 

 ment, and also the action of different reducing materials on osmic 

 acid. The latter experiments may be of' value in differentiating 

 tissues under the microscope. Since the subject appeared to Ije 

 extremely obsdure, and the statements contradictory, we thought it 

 would be of interest to record the results of our experiments at the 

 present stage. 



Summary. 



The black substance formed by the reduction of osmic acid by 

 olein in tissue-staining was found to he a hydrated form of osmium 

 dioxide, OsOi, and not metallic osmium, as has sometimes been 

 stated. 



BiBLIOGEAPHY. 



1. RoscoE & ScHOELEMMEE. — Treatise on Chemistry, ii. (1913), p. 1353 ; 



J. N. Feiend, Inorganic Chemistry, ix. part 1, p. 219 (1920). 



2. HoFMANN, K. A. — Lehrbuch der anorganischen Chemie, 1919, p. 647. 



0. O. Ruff & H. Rathsbueg. — Ber. Deutsch. Chem. Ges., 1917, 1. pp. 484-98. 

 4. Beezelius. — Traite de Chimie, 1840 edit., iii. p. 29. 



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