60 SCIENTIFIC AMUSEMENTS. 



however, form large feathery crystals when properly heated. 

 Benzole acid is one of the best examples of this, when prepared 

 by cautiously heating the natural product gum benzoin, an exuda- 

 tion from the bark of a peculiar tree (Sty rax benzoin), occurring in 

 Sumatra, Siam, and other Eastern hot countries, something like 

 the sticky gum often visible flowing from the bark 

 of plum and peach trees in this country, but harder. 

 Procure two small glass shades or beakers (fig. 34) 

 of different sizes, so that one will slide within the 

 other, and cover over the mouth of the smaller one 

 with two or three folds of blotting-paper tied on 

 like the cover of a jampot, having previously placed 

 in it an ounce or two of coarsely-powdered gum 

 benzoin. Now slide the wider shade over the other 

 s one ) an( i place the lower one in a small saucepan 

 or tin-pot full of sand nearly up to the level of 

 the lower edge of the upper shade. Cautiously heat the " sand- 

 bath " thus formed by means of a lamp ; the benzoic acid contained 

 in the gum will be gradually volatilised along with small quantities 

 of tarry or oily matter ; the latter will mostly be absorbed by the 

 paper, but the benzoic acid vapour will pass through the pores of 

 the paper, and condense in the upper shade to beautiful light 

 feathery crystalline plates of peculiar odour. When the operation 

 is over these can easily be removed and bottled for use ; the 

 sublimed benzoic acid thus prepared is employed in pharmacy and 

 for other purposes. 



Expt. 54. Frosted Trees. Fix in a glass shade or cylindrical 

 jar a twig or small branch of any garden shrub, and then place 

 the jar mouth downwards over an iron plate on which some 

 benzoic acid is thrown, and quickly heat the plate, so as to cause 

 the acid to sublime ; the crystals will deposit on the leaves and 

 stem of the branch, giving a pretty frosted appearance. It is 

 usually best to heat the plate strongly first, then throw on the 

 benzoic acid, and immediately place the jar over it to catch the 

 vapours. 



