190 PROCEEDINGS OP THE SCIENTIFIC ASSOCIATION. 
Specific gravity of soil 
One cubic foot of the soil weighs . . . 
One acre to a depth of 6 inches weighs 
2*3554 
... 146*79 lbs. 
3.197,086 lbs * 
One acre, weighing say three million pounds, contained 
the following quantities of the more important constituents 
Silicic anhydride (soluble) 
Phosphoric anhydride 
Calcium oxide 
Magnesium ,, 
Sodium „ 
Potassium ,, 
21 lbs.f 
3,492 „ 
10,839 „ 
8,064 „ 
1,329 „ 
2,961 „ 
For comparison with the above figures the following 
computations of the quantities of those ingredients in home 
soils from the Westindies (Antigua) have been made from 
the analysis of Dr. Angus Smith, F.R.S. ( Sugar Cane , vol. i,, 
p.3). 
Three million pounds of soil contained the following numbers of 
pounds of constituents soluble in hydrochloric acid ; — 
■vt Silicic Phosphoric 
* Anhydride, Anhydride. 
Calcium 
Magnesium 
Sodium 
Potassium 
Oxide. 
Oxide. 
Oxide. 
Oxide. 
1. 18399 263 
29097 
2998 
6441 
169 
2. 2662 — 
37187 
6753 
7657 
— 
3. 3814 — 
52506 
9285 
9319 
1145 
* This estimate refers only to th§ weight of an acre of the soil free 
from porosity — i.e f , in a perfectly solid mass. The above extent of 
soil, as it exists naturally in its comparatively loose state, would 
weigh much less, say from 2,000,000 to 2,500,000 lbs. 
f The determination of the amount of soluble silicic anhydride 
was carefully performed twice. In the first case the hydrochloric 
acid solution of 300 grammes of soil was evaporated to complete 
dryness, heated again with hydrochloric acid in the usual way, and 
the silicic anhydride collected on a filter and weighed. Its weight 
was only 0*002 gramme. The experiment was repeated on the hy- 
drochloric extract of 50 grammes of soil, but the silicic anhydride 
obtained (if any) was unweighablje, 
