SALTS. 



freeze in intense frosts. I have repeatedly wit- 

 nessed in the case of culinary vegetables, such 

 as cabbages, broccoli, &c., that, while the pro- 

 duce of the unsalted portions of the ground 

 were half-killed by the frost, the salted portions 

 have totally escaped. Many salts have also 

 the property of retarding the evaporation of the 

 moisture of the soil ; others absorb it from the 

 atmosphere, or are of the class of deliquescing 

 salt; such are the common salt, chloride of 

 calcium, chloride of magnesia, cubic petre, or 

 nitrate of soda, &c., which, in consequence, 

 when they are used as fertilizers, they increase 

 this property, so valuable and so essential to 

 all cultivated soils. Thus I found by some 

 experiments upon a rich soil near Maldon, in 

 Essex, worth 42s. per acre, that 1000 parts, 

 dried at a temperature of 212, absorbed in 18 

 hours, by exposure to air saturated with moist- 

 ure at a temperature of 62, 25 parts. But 

 1000 parts of the same field, which had been 

 dressed with 12 bushels of marine salt per 

 acre, under the same circumstances gained 27 

 parts ; and 1000 parts of the same soil, which 

 had been dressed with 6 bushels per acre, 

 gained 26 parts. The attraction of some sa- 

 line substances for the moisture of the atmo- 

 sphere is very considerable. I found that 1000 

 parts of refuse salt manure, dried at 212, ab- 

 sorbed in 3 hours, by exposure to air saturated 

 with moisture at 60, 49$ parts. 1000 parts of 

 the sediment or pan-scratch of the salt-makers, 

 gained 10 parts; 1000 parts of Cheshire crushed 

 rock-salt, 10 parts; 1000 parts of gypsum, 9 

 parts. Chloride of calcium is so powerfully 

 deliquescent, that it absorbs sufficient moisture 

 from the air to dissolve in it and form a solu- 

 tion. Dr. Marcet found that 288 grains in 124 

 days absorbed 684 grains of water. 288 grains 

 of nitrate of lime, a salt found in some of the 

 richest alluvial soils of the East, absorbs in 147 

 days 448 grains. Carbonate of potash, another 

 saline fertilizer, also absorbs moisture. Now, 

 it is \vorthy of the farmers' notice, that chlo- 

 ride of calcium is the very salt which is pro- 

 duced in such abundance by the decomposition 

 cf common salt by lime, in the way so suc- 

 cessfully recommended first, by the old Ger- 

 man chemist Glauber, by Mr. Hollingshead, 

 Mr. Bennett, and Sir Charles Burrell (See SALT 

 and LIME); for, by the slow action carried on 

 for three months by these substances on each 

 other, this salt and soda are produced by the 

 decomposition; and it is not improbable that 

 when these salts are present in the juices of 

 plants, that by this means the attractive powers 

 of their leaves and roots for aqueous vapour 

 may be increased. Davy alludes to these es- 

 sential, yet too little understood powers of ab- 

 sorption possessed bv vegetables, when he says 

 (Lectures, p. 207), "In very intense heats, and 

 when the soil is dry, the life of plants seems 

 to be preserved by the absorbent power of their 

 leaves; and it is a beautiful circumstance in 

 the economy of nature, that aqueous vapour is 

 most abundant in the atmosphere when it is 

 most needed for the purposes cf life, and that 

 when other sources of its supply are cut off, 

 this is most copious." 



Of the salts of ammonia, as I have i i another 

 place remarked, carbonate of ammonia has 

 123 



SALTS. 



been detected in the Chenopodium olidum by 

 Messrs. Chevalier and Lasseigne ; and it pro- 

 bably exists in other plants which are distin- 

 guished for their powerful disagreeable odour. 

 Muriate of ammonia has been found in woad 

 by M. Chevreul. The salts of ammonia are in 

 general exceedingly fertilizing in their effects 

 upon vegetation. Soot owes part of its efficacy 

 to the ammoniacal salts it contains. The liquor 

 produced by the distillation of coal contains 

 carbonate and acetate of ammonia, and this 

 liquid of the gas-makers is a very good manure. 

 "In 1808," says Davy, "I found the growth of 

 wheat in a field at Roehampton assisted by a 

 very weak solution of acetate of ammonia." The 

 experiments of Mr. Robertson with soot clearly 

 show the fertilizing effects of the soluble por- 

 tion of it. He mixed together, in order to form 

 a liquid manure, six quarts of soot in a hogs- 

 head of water. "Asparagus, peas, and a va- 

 riety of other vegetables," says this intelligent 

 horticulturist, "I have manured with this mix- 

 ture, with as much effect as if I had used solid 

 dung." Care must be taken, however, in using 

 this and all other liquid fertilizers, not to make 

 the solutions too strong: it is an error into 

 which all cultivators are apt to fall in their 

 early experiments. Even Davy was not an 

 exception, since, from making his liquids too 

 concentrated, he obtained results which widely 

 differed from his later experiments. There is 

 no doubt but that the salts of ammonia, and all 

 the compound manures which contain them, 

 have a very considerable forcing or stimulat- 

 ing, or, perhaps, from their decomposition, 

 nourishing effect upon vegetation. In the ex- 

 periments of Dr. Belcher upon the common 

 garden cress, by watering them with a solution 

 of phosphate of ammonia, the plants were 15 

 days forwarder than plants growing under 

 similar circumstances, but watered with plain 

 water; and he also describes the experiments 

 of Mr. Gregory, who, by watering one-half of a 

 grass field with urine, nearly doubled his crop 

 of hay. Other testimonials in support of the 

 fertilizing powers of the salts of ammonia are 

 furnished by Mr. Handley. 



Of the mode in which ammonia operate* 

 upon plants, a late valuable work on organic 

 chemistry, by M. Liebig, abounds with ob- 

 servations, with some of which I cheerfully 

 and cordially agree. To understand these re- 

 marks, however, the farmer must remember 

 that ammonia is composed, according to the 

 analysis of Davy, of hydrogen 74 parts, and 

 azote or nitrogen 26 parts. "The nitrogen of 

 putrefied animals," he observes, "is contained 

 in the atmosphere, as ammonia in the form of 

 a gas, which is capable of entering into com- 

 bination with carbonic acid, and forming a 

 volatile salt. Ammonia in its gaseous form, 

 as well as all its volatile compounds, are of 

 extreme solubility in water. Ammonia, there- 

 fore, cannot remain long in the atmosphere, as 

 every shower of rain must condense : t, and 

 convey it to the surface of the earth : thence, 

 also, rain-water must at all times contain am- 

 monia, though not always in equal quantity. 

 It must be greater in summer than in spring 

 or in winter, because the intervals of time be- 

 tween the showers are greater; and, where 

 4 N 2 977 



