THE society's NOTE-BOOKS. 193 



To prevent the Growth of Mildew on Dry Mounts, it is useful 

 to paint the specimen, and the interior of the cell, with a solution 

 of Carbolic Acid, or Corrosive Sublimate in spirit, before mounting. 



H. F. Parsons. 



Dr. Hunt's American Cement for Ringing-Slides. — An 



American correspondent has sent me the following recipe for 

 making the cement, so effectually used by professional micros- 

 copists, and which some have regarded as a trade-secret : — 



" Take some Zinc White as sold for painters' use, drain off the 

 oil, and mix with Ca?iada Balsam dissolved very thin with 

 Chlorofortn. If it does not flow freely from the brush, add a little 

 Turpentine. The mixture should be about the thickness of cream, 

 and kept in a bottle with a glass cap. An old glass-capped spirit- 

 lamp, fitted with a cork, in which the brush is fastened, is very 

 convenient for holding it, and is always ready for use. 



J. Ford. 



Having sealed the slide with the above cement, paint on it 

 with artists' oil-colours, thinned if necessary with Turpentine, and 

 when dry, varnish it with very dilute Balsam, to give it a gloss. 



F. J Allen. 



Fatty Acids to prepare for the Microscope. — Boil up the fat or 

 oil with solution of Caustic Soda or Potash (Liq. Sodce or Liq. 

 Potassae) until the alkali is quite saturated and refuses to absorb 

 any more fat. When it has cooled filter it and add dilute Sul- 

 phuric or Hydrochloric Acid (stirring and warming at the same 

 time) until no more fatty acid separates. Boil for a second or two, 

 then set aside to cool. When cold, the fatty acid will be found in 

 a solid mass on the surface, and the liquid part may be thrown 

 away. 



It is well to boil the acid in fresh water to purify it ; when, on 

 cooHng, it will be practically pure. N.B. — If the Liq. Potassse or 

 Sodae is too strong, it will refuse to saponify. 



To get Crystals, it is simply necessary to melt a small quantity 

 on a slide, and spread it very thin ; it crystallizes on cooling, and 

 must be mounted " dry." 



F. J. A. 



