270 TECHNOLOGY OF DIATOMS. 



Slyrax. — We have here a true balsam of a composition very 

 complex, obtained from the Styrax orientalis. This balsam, of a 

 deep brown colour, contains cinnamic acid, a near neighbour to 

 benzoic acid, as well as numerous impurities, from which it must 

 be freed. This is the method that I employ, and which is mainly 

 that described by M. le Professor J. Brun for the preparation of 

 Tolu. 



The balsam of commerce is boiled with enough water (about 

 twenty times the volume of the balsam under treatment), renewed 

 twice ; the floating mass, very soft after it is cooled, is then 

 exposed in saucers and placed on a stove till it becomes brittle. 



The mass is then dissolved in benzole, then filtered twice in a 

 funnel, of which the upper part is covered with a plate of glass. 

 The filtered portion is exposed, protected from dust, until by the 

 evaporation of the benzole it acquires the desired consistence — a 

 semi-fluid. The index of refraction of styrax is i"62. 



Balsam of Tolu, Liqtdd Amber. — It was M. le Professor J. 

 Brun, of Geneva, who first proposed to employ balsam of Tolu to 

 replace Styrax. Balsam of Tolu is obtained by making incisions 

 in the bark of the Toluifera balsamum. Tolu is less dark than 

 Styrax and is prepared in the same manner. In commerce you 

 can meet with Tolu that has been deprived of the benzoic acid by 

 washing with water. In this case, it is only necessary to dry the 

 mass on a stove without further washing. The index of refraction 

 of Tolu is I '64. 



Liquid Amber — which is extracted from Liquidamber styraci- 

 flua — is found in commerce in a fluid or viscous form. The 

 latter is the only one for our use ; in other respects, it has a close 

 analogy with Tolu, without possessing any advantages. 



Unless the various balsams (Canada balsam alone excepted) 

 are prepared with great care, and completely free from the acids 

 they contain, you run the risk, after a certain time, of seeing 

 numerous crystals form in the mass — crystals that often make the 

 preparation unfit for study. Their index of refraction is the reason 

 for employing them, but their brown colour is disagreeable, and it 

 is this, above all, that has always made me prefer the Monobromide 

 of Naphthaline mixed with Canada balsam. Diatoms are mounted 

 in Styrax Tolu in the same manner as in Canada balsam. - 



