362 
Analyses of Books. 
[June, 
painting, we come to a treatise on resinous and gummy articles, 
extending to no fewer than seventy-five pages. It may, of course, 
be objected that there are thus included under one head products 
differing essentially in their chemical relations. The characters 
of these two groups are, however, given in detail at the outset, so 
that practically no inconvenience can arise. There are a few 
remarks on the origin of gums which were formerly supposed to 
be secretions. Recent investigations have proved that they are 
formed from the whole tissue of the cell-walls. It may, by the 
way, be suggested that gum is a morbid produCt. The writer 
admits that gums are yielded most abundantly when plants are 
in a sickly state. 
Under gum arabic we find mention of a gum furnished by 
several Australian species of Mimosa. The trees are much more 
rapid in their growth than the cognate species in Africa, and 
there is reason to believe that the Australian gum might become 
the subject of a large trade, especially as its mucilage when dry 
is less liable to crack than that of some other kinds. 
Balata, a gum-resin of the caoutchouc class, though in con- 
siderable demand, appears less and less in the market owing to 
the difficulty of procuring a regular supply. In America it is 
put to the singular purpose of a chewing material. 
Under dextrine we find mention of the ' faCt that experiments 
to produce dextrine from cellulose have proved failures. The 
attempt, however, should not be abandoned, as the value of 
cellulose is very much lower than that of starch, the present 
starting-point of the raw material. We do not see any reference 
to the most important impurity, sand or grit. 
It is a somewhat remarkable faCt that the various resins used 
in compounding incense seem all to contain more or less benzoic 
acid. It is hence possible that their original use was as disin- 
fectants. 
Concerning gutta-percha there is much interesting information. 
It appears that unless the tree is cultivated and a method is 
brought into use of collecting its milky juice without killing it, 
the supply must soon be at an end. The article is adulterated 
on the spot by the collectors. In Borneo about 20 per cent, of 
scraped bark is added, to which its reddish colour is due. It is 
even said that the Chinese middle-men who buy it from the 
gatherers, refuse to take it in its pure condition. Gutta-percha 
appears to undergo no change by twenty years exposure to sea- 
water, though if alternately wetted and dried, it rapidly deterior- 
ates, a faCt which has almost put an end to its use for jugs, 
syphons, funnels, carboys, &c. 
Caoutchouc is exposed to the same peril as gutta-percha, the 
demand is rapidly extending, the wild supply is as rapidly de- 
creasing, and attempts at its cultivation, though not altogether 
wanting, are scarcely made on the scale and with the vigour that 
are required. 
