On the I\itrate of Soda. 



123 



may have occasioned a similar failure which you mention to have occurred 

 on yourown farm. An objection has been made to the use of the nitrate, 

 that its effect lasts for one year only. If it brings back its own cost, how- 

 ever, in the year, the objection is not just, at least when it is applied to 

 grass ; for we must not forget that an increase of food for stock once 

 raised on grass-land by any fresh means is a new capital created, which 

 circulates between the stock and the land, giving more dung to the soil, 

 and, again, more food to the additional animals which are maintained on 

 that soil, for as many years as the farm continues to be well managed. 

 Whether it exhaust a soil by increasing the crop of grain is a more 

 difficult question, which cannot be answered without further observa- 

 tion. But the investigation of its effects is, I think, as likely to ad- 

 vance scientific as practical farming. Hitherto manures have been 

 classed rather loosely as real or nutritious manures, such as dung, 

 and stimulating manures, such as lime and other minerals ; w^hich last 

 are supposed not to support the plant directly by affording it food, 

 but indirectly, by exciting other substances, that are thus rendered 

 capable of giving nourishment to it. German vrriters, however, now 

 maintain that dung itself acts not by any power which it possesses as 

 having formerly been a part of living bodies, animal or vegetable, but 

 as uniting those chemical elements, some of them mineral, which con- 

 stitute the food of plants; and that a compound of these elements, 

 artificially brought together, would act precisely in the same manner as 

 dung. Dr. Liebig, who is regarded as the first living authority on 

 organic chemistry, maintains this view in the important work he has just 

 published on " Chemistry in its application to Agriculture," and goes 

 far to prove it. This is, in fact, the great question, if it still be a question, 

 in agricultural chemistry. But the substance we are considering throws, 

 I think, some light on this point and on the operation of other manures. 

 It is now admitted that the most active principle of farm-yard dung is 

 the urine that is mixed in it. When this urine, which is the liquid- 

 manure of the Flemings, is applied to growing crops as a top-dressing, 

 it gives a dark colour to the grasses (including those grasses which bear 

 grain, that is, common corn) ; it has a tendency to lengthen, but weaken 

 the straw, — to increase the bulk, but diminish the weight, of the grain. 

 I need not remind you that this liquid, w^hen putrified, contains much 

 ammonia : soot, I believe, acts in the same manner, and also contains 

 much ammonia. The refuse-liquor of gas-works was mentioned in the 

 first Number of our Journal as producing the same dark colour and 

 active growth in barley. I have tried it this year in consequence, and 

 found it to act in the same manner on carrots. The chief ingredient of 

 this liquor is also ammonia, as may be perceived by its pungent smell. 

 It appears clear, therefore, that one active principle of these three very 

 different manures is that substance in which they agree, namely, am- 

 monia. But the nitrate of soda enables us, I think, to go a step further. 

 Ammonia is a combination of nitrogen with hydrogen : either of these 

 might be the source of its power over vegetation ; but we have seen that 

 saltpetre, or nitrate of potash, and cubic saltpetre, or nitrate of soda, act 

 upon crops in the same peculiar manner with fermented urine, with soot, 

 and with gas-liquor. These last, however, do not contain hydrogen, and 



