GARDENING AS A SCIENCE. 
155 
carbon, 52-883; oxygen, 23*872 ; hydrogen, 7-540; azote, 15*705. In Liebig's 
Animal Chemistry, a most luminous view is taken of this analogy. 
5. Gluten is another of the azotised products of vegetables : it is found, 
according to Davy, " in acorns, chesnuts, horse-chesnuts, apples, and quinces ; 
barley, rye, peas, and beans ; likewise in the leaves of rice, cabbage, cresses, hem- 
lock, borage, saffron ; in the berries of the elder and the grape. Gluten appears to 
be one of the most nutritive of vegetable substances ; and wheat seems to owe 
its superiority to other grain, from the circumstance of its containing it in larger 
quantities." It is a tenacious, ductile, elastic substance, obtained by washing 
away the starch, from a paste made of wheat flour, and kneading it under a small 
stream of water. 
Gluten of the grape is a chief agent also in the vegetable fermentation of wine. 
8. Tannin is the astringent principle of a vast number of vegetable products, 
of which gall-nuts and oak-bark become the most familiar examples. " The 
characteristic property of tannin is its action upon solutions of isinglass and jelly. 
Skins consist almost entirely of jelly, or gelatine in an organised state, and are 
soluble by the long-continued action of boiling water." By the process of tannincf 
the gelatine is fixed by the tannin in the fibrous tissue of the skin. When wine 
is fined by isinglass, the floating tannin is attracted, and falls down in the state of 
an insoluble compound of isinglass and tannin. 
We need not enlarge on this branch of vegetable products, but shall come at 
once to the consideration of those not soluble in water, and first of 
No. 12. Wax, This is found pure in the leaves of some trees, and seems to be 
of the same nature as that produced by the bee. 
The products are stated to be 
Carbon ........ 81-;84 
Oxygen 5-554 
Hydrogen ........ 12-672 
or otherwise, carbon 81*784, oxygen and hydrogen in the proportions of water 
6 '300 — hydrogen in excess, 11*916. 
13. Resins differ from wax by being more highly oxygenised. 
Common Resin, usually pronounced Rosin, is a production of the fir-tree. 
Pure" resin is insoluble in water, either hot or cold ; but very soluble in alcohol. 
When a solution of resin in alcohol is mixed with water, the solution becomes 
milky ; the resin is deposited by the stronger attraction of the water for alcohol. 
By analysis it appears that different resins develope different proportions of the 
three elements. Thus, 
Common Resin is estimated at— Carbon 75-944 
Oxygen and Hydrogen as in water . . 15-156 
Hydrogen in excess .... 8*900 
