718 SUMMARY OF CURRENT RESEARCHES RELATING TO 



arc not awaro of tho fact. Mr. A. C. Cole recently brought us some 

 slides of Heliopelta, Coscinodiscns, Trinacria, and Triceratium, mounted 

 in tins medium, which (at any rate for the diatoms in question) prove 

 that cassia oil can hardly be surpassed as a mounting medium. Tho 

 clearness with which the markings arc shown is very remarkable. 

 The refractive index of cassia oil is about 1 • 640. 



Mounting with Carbolic Acid.* — Mr. T. Steel has varied some- 

 what the process of carbolic-acid mounting, described by Mr. J. E. Y. 

 Goldstein. f 



If the object is an insect, it is treated with potash or soda in the 

 usual manner, to render it transparent ; it is then rinsed in water and 

 passed into spirit. The carbolic acid is prepared as follows : — Take, 

 say, 1 oz. of Calvert's pure solid acid, and melt it by placing the 

 bottlo in warm water ; when thoroughly fluid, add about 30 drops of 

 spirit, shake well, and allow to cool ; if it crystallizes again, melt as 

 before, and add 10 or 15 drops more spirit, and again shako and allow 

 to cool. Now melt a portion of balsam on the slide, and removo 

 air-bubbles ; heat the balsam until it is sufficiently evaporated to 

 becomo firm on cooling ; allow to cool. Place three pieces of thin 

 wire as supports for the cover-glass. In the meantime the object 

 should have been removed from the spirit and placed in a short test- 

 tube containing some of the carbolic acid, and allowed to soak until 

 quite saturated; or it may be gently boiled, which is the quickest 

 way. When boiling, the tube should be kept shaken. A few seconds 

 is all the heating required. This boiling is a capital way of getting 

 rid of air-bubbles, and, if necessary, the tube should be allowed to 

 cool and again heated, and this will seldom fail to displace any 

 persistent bubbles. The object being now thoroughly permeated by 

 the acid, the tube is allowed to cool. A drop of carbolic acid is now 

 placed on the surface of the hard, cool balsam on the slide by means 

 of a dipping-tube; the object is then taken out of the tube on a 

 mounted needle, or the contents of the tube emptied into a little dish, 

 and the object taken out and at once placed in the drop of acid on 

 the slide and arranged as desired. The cover-glass is taken in the 

 forceps, and a drop of the acid spread on its under surface. Should 

 any air-bubbles appear in this drop of acid during the spreading, 

 they are best got rid of by holding the cover-glass for a moment over 

 the lamp. The cover-glass is held in place by a light wire clip ; and 

 the excess of acid absorbed by bibulous paper. 



When the excess has been absorbed, the slide is gently warmed, 

 and as the balsam softens, the spring clip presses the cover-glass 

 down into position. The slide, with the clip still on, is baked in the 

 usual manner. Six to twelve hours is sufficient baking for most slides, 

 but that depends on the degree to which the balsam has been evapo- 

 rated before placing the object. When the operation of baking has 

 been satisfactorily accomplished, the slides are allowed to cool, always 

 keeping on the clip till they are quite cold. 



* Scientif. Enquirer, i. (18SG) pp. 41-3. 

 t See this Journal, iii. (1880) p. 858. 



