56 THE AMERICAN MONTHLY [Feb 



shown by the comparisons with the silica standard. 



Different preparations of silica fromdiatomaceoas earth 

 on the other hand, gave practically uniform results. Mi- 

 croscopical examination of the silica and kaolins showed 

 that the particles of silica obtained by grinding the dia- 

 toraaceous earth were quite uniform in size, while the par- 

 ticles of aluminum silicate showed much greater varia- 

 tions. In some of the samples the kaolin particles were 

 much finer than in others, which accounted for the great 

 variations in turbidity in different aamples of kaolin. 



The silica method of determining turbidity has been 

 employed with a large number of v^aters, in which near- 

 ly every form of turbidity has been represented, and as 

 a general laboratory method it commends itself for sim- 

 plicity, uniformity, and accuracy. 

 Mt. Prospect Laboratory, 

 Brooklyn, N. Y. 



Notes on Microscopy. 



F. SHILLINGTON SCALKS, F.R.M.S. 



••Soloid'' Microscopic Stains. — The tendency of solutions 

 of the aniline dyes to decompose is well known, and has 

 been a fruitful source of trouble to microscopists. Messrs. 

 Burroug-hs, Welcome and Compau}', London, obviate this 

 danger by supplying certain stains not only in a drv state, 

 but in tabloid form, each tabloid, or, as the makers call it, 

 "Soloid," being of known strength and requiring only to 

 be dissolved in water or alcohol to produce a solution of 

 equally definite concentration. The stains at present sold 

 are Eosin, Bismarck brown, Fuchsine, gcntain violet, and 

 Methylene Blue. Each "Soloid" contains one grain, and 

 can be obtained from the microscopical opticians in tubes 

 of six "Soloids" for the modest price of sixpence. The in- 

 structions given with the stains are so clear and practical 

 that we cannot do l)ctter than reproduce one or two exam- 

 ples. A saturated watery solution of fuchsine, methylene 



