580 SUMMARY OF CURRENT RESEARCHES RELATING TO 



however, be borne in mind that the sole advantage of phosphorus is 

 its high refractive index = 2 • 1. If it is diluted to 1 • 7, no benefit is 

 derived from its use over bisulphide of carbon or other substances 

 whose refractive index = 1 • 7, and they should therefore be used in 

 preference. Dr. Morris's note, however, contains some useful hints. 



" Having seen several specimens of diatoms mounted in phos- 

 phorus and bisulphide of carbon, I am under the impression that the 

 solution is too strong for the purpose required, and as I have mounted 

 some hundreds of slides in the strong and weak solutions, I have come 

 to the conclusion that the weak solution is the best and safest for 

 mounting minute objects, such as the Diatomaceae. 



" The solution I use is made as follows : — Take one ounce of car- 

 bon bisulphide and put it into a wide-mouthed stoppered bottle, and 

 add about two or three drachms of phosphorus piece by piece, taking 

 the precaution to previously absorb all the moisture from its surface 

 by placing it on blotting-paper for a second or two. When all is dis- 

 solved, filter through white filtering-paper and a glass funnel into 

 another bottle (narrow-mouth stoppered), wash the filter with a little 

 carbon bisulphide, and when filtered place the filter in a basin of water 

 until there is time to burn it in the fire. 



" Having made and filtered the solution, take a small piece of 

 white blotting-paper about an inch square, and with a glass rod put a 

 drop of the solution on the paper and watch the effect. If it flares 

 up with a yellow flame it is too strong, and requires more carbon 

 bisulphide added to it, but if it only smokes and carbonizes the paper 

 the solution is of the right strength. See that the stopper is well fixed 

 in the bottle, and put it away for a day or two. If any sediment has 

 formed in the meantime, filter once more, using the same precautions 

 with the filter as before. 



" If the solution is made according to the above directions, it will 

 be always ready for use and keep for months. 



" To make cement for the cover-glass, take of good isinglass one 

 ounce, put it into a saucer, add a few drops of water from time to time 

 until the isinglass is moistened but not pappy. Put about two ounces 

 of glacial acetic acid into a porcelain capsule, place it over a spirit- 

 lamp, and bring the acetic acid to boiling-point. Add the isinglass 

 by degrees until the whole is dissolved, keeping the mixture constantly 

 stirred. Boil until a spot placed upon a slip of glass becomes solidified 

 when cold. When sufficiently boiled, put it away in a wide-mouthed 

 bottle, using a cork for a stopper. A small quantity for constant use 

 may be kept in a two-drachm bottle. This must always be warmed in 

 hot water before applying it. 



" The diatoms being fixed on the cover, see that the following 

 articles are at hand : — A small bottle of carbon bisulphide, a glass 

 pipette four inches in length terminating in a fine point, a few pieces 

 of blotting paper one inch by half an inch, small camel-hair brush, 

 mounted needles, a small basin, and a turntable. 



" First gently warm the slide, centre it on the turntable, warm 

 the cover-glass and place it on the slide, wash the pipette with the 

 carbon bisulphide, then with the pipette take up a small quantity of 



