SOOLOGY AND BOTANY, MICROSCOPY^ ETC. 923 



Microscopical Examination of Volcanic Ash from Krakatoa.* — 

 Mr. J. Joly in preparing this dust for the Microscope found that mere 

 shaking up with water, and pouring off before complete settlement, 

 served only to remove the lighter fragments of pumice, and that com- 

 plete separation was only readily effected by the following method : — 



Into a glass tube 1 m. long and about 4 cm. in diameter, closed at 

 one end and filled with water to the brim, the partially cleansed dust 

 is introduced and allowed to settle, A strip of glass is now pressed 

 on the open end, and the whole rapidly inverted into a shallow dish 

 containing water. The denser particles descending most rapidly 

 through the column of water in the tube, reach the dish first. When 

 the more slowly moving particles are observed to have nearly attained 

 the dish, a movement of the tube to one side effects the desired 

 separation. 



The author found that the constituents of the ash presented under 

 the Microscope a spectacle of the most extreme interest and beauty, 

 especially with polarized light. 



Examination of Potable Waters.f — The method recommended 

 by Herr J. W. Gunning for the chemical examination of water consists 

 in adding to a litre of the water enough ferric chloride to corresi^ond 

 with about 5 mgrms. of iron. The ferric chloride should be as 

 nearly neutral as possible. Under these conditions, ammonia, nitrites 

 and nitrates are left in solution, whilst other nitrogenous substances 

 are carried down with the precipitate of ferric hydroxide. By heat- 

 ing this with soda-lime the nitrogen of these compounds is obtained 

 as ammonia. By this treatment cloudy water is completely clarified 

 and yellow moor-water decolorized. The process has been applied 

 with success on a large scale in Holland for the purification of drinking- 

 water, especially during diarrhoea and cholera epidemics. 



In the bacteriological examination of water, the author prefers to 

 develope a pjure culture in a liquid medium rather than in the solid 

 medium recommended by Koch. The water to be tested is mixed 

 with a clear sterilized yeast decoction. By sterilizing this again, 

 certain bacteria arc either killed or rendered inactive, while the others 

 from their superior vitality survive and develope. By a process of pro- 

 gressive sterilization, beginning at low temperatures and gradually 

 ascending, pure cultures are obtained. 



Removal of Micro-organisms from Water.;}:— Dr. P. F. Frank- 

 land has investigated the efficiency, as regards the removal of micro- 

 organisms, of methods of water-pixrification depending upon (a) fil- 

 tration ; (6) agitation with solid particles ; (c) subsidence, and (d) 

 chemical precipitation (Clark's process). The mctliod of investigation 

 consisted in determining the number of organisms present in a given 

 volume of the water before and after treatment, the determinations 

 being made by Koch's process of gelatin- culture on glass plates. 



• Scieiitif. Troc. R. DuLlin Soc, iv. (1885) pp. 291-9 (2 1)1h.). 

 t Ch<m. Ceiitr., 1881, pp. 151-2. Heo Joiun. Cliem. ISoc. — Abatr., xlviii. 

 (laHro p. 841. 



X I'roc. Roy. Soc, xxxviiL (1885) pp. 379-93, 



