ON MANURES. 27 



proved ; that the rain will wash in the salts, while the sun 

 only exhales the water ; that, when spread upon the surface, 

 the soil also thus becomes gradually impreg^nated with its juices ; 

 and that clay land in particular is rendered mellow and free 

 to plough. Thus with many it is the practice to carry out 

 yard-dung in its long and hot state, and to suffer it to lie both 

 upon arable and grass land for perhaps a month or six weeks 

 after being spread, before it is ploughed m, though it is 

 knowledged to encourage the growth of weeds. Others cover 

 it with a slight coat of mould. On the other hand, although 

 the process of fermentation, by disengaging a quantity of car- 

 bonic acid and ammonia, causes an evaporation, by which the 

 bulk of the manure is much diminished, yet its power is 

 thought to be thus increased. This apparent diminution in 

 bulk has indeed been too much insisted on by the opponents 

 of rotten dung, as proof of its decrease in value ; for, although 

 the size of the heap thus evidently becomes smaller, yet its 

 cubical contents are, by its condensation, increased in weight.* 

 After about six weeks it assumes a saponaceous, greasy ap- 

 pearance, in which soft and sappy state, when neither fresh 

 nor too rotten, but in the medium between those states, it is 

 generally applied to the land by the best farmers. When 

 very rotten, its effect is more immediate and powerful ; but 

 when only moderately rotted, its efiect, though more gradual, 

 is found to be more durable. 



On this subject of evaporation, which has justly engaged so 

 much of the attention of scientific agriculturists, we, how- 

 ever, add the following extracts from the work of Von Thaer, 

 whose practical knowledge cannot be *too highly appreciated. 

 He says, that not only does theory teach us, but during his 



*The weights of putrescent manures will depend much upon the progress 

 of their decomposition at tlie time, as well as the proportion of moisture 

 which, from accident or particular treatment, they may contain. From an 

 experiment on the subject, recorded in the Farmer's Magazine, we learn 

 that the comparative weight of the following substances, was as follows :— 



cwt. qrs. lbs. 



One cubical yard of garden-mould . . 19 3 25 



Ditto of water . . . . : 15 7 



Ditto of a compost of earth, weeds, lime, and dung, that 



had lain nine months, and been turned over 14 5 



Ditto of new dung . . . ... 9 3 18 



Ditto of leaves and sea-weeds . . . 9 7 



Thus, a cubic yard of water is to that of new dung nearly as 3 to 2.— vol. 

 xiv. p. 162. Von Thaer calculates the weiglit of a cubic foot of any strawy 

 farm-yard manure at only about 46 lbs. ; while one which has been partly 

 decomposed will weigh from 56 to upwards of 60 lbs., without being com- 

 pressed. — Principes Raisonncs d' Agriculture, torn. ii. p. 326, 



