Balata and the Balata Industry. 209 
The passage quoted by Mr. Francis from Mr. Mel- 
ville's paper, which was copied in the preface of the 
Exhibition Catalogue of British Guiana does not say 
what greater proportion of milk or balata was obtained 
from the bark by the system of steam working, than by 
that of tapping and natural bleeding. In relation to this 
question, Mr. FRANCIS has carried out experiments on 
the bark of a tree that was felled for the purpose, part 
of the bark having been bled and part not bled. This 
experiment seems to show that only a trifling portion of 
the milk is obtained by bleeding. Mr. FRANCIS says : 
" A sample of the milk measuring about one pint, and two samples of 
bark, one taken from the place where the tree was tapped, the other 
from an untouched part, were brought to Georgetown. A third sample 
of the bark taken from the tree about a fortnight after it had been felled 
was sent to the laboratory by Mr. McTurk. 
" The milk had a specific gravity of 0*9868 and yielded by evapora- 
tion 6o - i8 per cent, of solid matter forming the ordinary balata gum of 
commerce. The amount of mineral matter in the milk was 0*48 per 
cent, To determine the quantity of gum by precipitation with alcohol 
the milk was diluted to about thrice its bulk with water and alcohol of 
40 over proof was added until no further effect was produced. The 
coagulum was removed and alternately boiled with water and strongly 
squeezed several times to remove foreign substance, and was finally 
heated in the hot air-oven at ioo° C until all moisture was removed and 
it ceased to lose weight. In this way the proportion of gum obtained 
was reduced to 52' 13 per cent., thus showing that a quantity of foreign 
matter (about 805 per cent, of the milk or 13*30 per cent, of the dry 
solids) is incorporated with the gum as usually prepared. Nevertheless, 
the ordinary gum has a higher commercial value than the precipitated 
product, so that the foreign matters present add to the value of the 
crude gum not only by this weight, but apparently by favourably modi- 
fying the properties of the pure substance. Pure precipitated balata 
gum is white, or greyish white in colour and of very hard and tough 
consistency and it is entirely soluble in bisulphide of carbon ; whereas, 
the crude gum prepared by evaporation or simply drying, is of a more 
BB 
