650 



FARMER S' REGISTER. 



[No. n 



would be formed in the process of vegetation ; but 

 the oats grew very feebly, and began to be yellow 

 before any flowers formed : the entire plants were 

 burnt, and their ashes compared with those from 

 an equal number of grains of oat. Less siliceous 

 earth was given by the plants than by the grains ; 

 but their ashes yielded much more carbonate of 

 lime. That there was less siliceous earth, I attri- 

 bute to the circumstance of the husk of the oat 

 being thrown off in germination ; and this is the 

 part which most abounds in silica. Healthy green 

 oats, taken from a growing crop, in a field of which 

 the soil was a fine sand, yielded siliceous earth in 

 a much greater proportion than an equal weight 

 of the corn artificially raised. 



The general results of this experiment are very 

 much opposed to the idea of the composition of 

 the earths, by plants, from any of the elements 

 found in the atmosphere, or in water ; and there 

 are other facts contradictory to the idea. Jacquin 

 states that the ashes of glass wort (^salsola soda,') 

 when it grows in inland situations, afford the ve- 

 getable alkali ; when it grows on the sea-shore, 

 where compounds which afford the fossil or ma- 

 rine alkali are more abundant, it yields that sub- 

 stance. Du Hamel found that plants which usu- 

 ally grow on the sea-shore, made small progress 

 when planted in soils containing little common 

 salt. The sun-ffower. when growing in lands 

 containing no nitre, does not afford that substance; 

 though when watered by a solution of nitre, it 

 yields nitre abundantly. The tables of De Saus- 

 Bure, referred to in the third lecture, show that 

 the ashes of plants are similar in constitution to 

 the soils in which they have vegetated. 



De Saussure made plants grow in solutions of 

 different salts, and he ascertained that in all cases 

 certain portions of the salts were absorbed by the 

 plant, and found unaltered in their organs. 



Even animals do not appear to possess the 

 power of Ibrming the alkaline and earthy sub- 

 stances. Dr. Fordyce found, that when canary 

 birds, at the time they were laying eggs, were de- 

 prived of access to carbonate of lime, their eggs 

 had soft shells ; and if there is any process for 

 which nature may be conceived most likely to 

 eupply resources of this kind, it is that connected 

 with the reproduction of the species. 



As the evidence on the subject now stands, it 

 seems fair to conclude, that the different earths 

 and saline substances found in the organs of plants 

 are supplied by the soils in which they grow ; and 

 in no cases composed by new arrangements of the 

 elements in air or water. What may be our ulti- 

 mate view of the laws of chemistry, or how far 

 our ideas of elementary principles may be sim- 

 plified, it is impossible to say. We can only rea- 

 son from facts. We cannot imitate the powers of 

 composition belonging to vegetable structures ; 

 but at least we can understand them : and, as far 

 as our researches have gone, it appears that in 

 vegetation compound forms are uniformly produced 

 fro'm simpler ones ; and the elements in the soil, 

 the atmosphere, and the earth, absorbed and made 

 parts of beautiful and diversified structures. 



The views which have been just developed lead 

 to correct ideas of the operation of these manures, 

 which are not necessarily the result of decayed 

 organized bodies, and which are not composed of 

 different proportions of carbon, hydrogen, oxygen, 

 and azote. They must produce their effect, either 



by becoming a constituent part of the plant, or by 

 acting upon its more essential food, so as lo render 

 it more fitted tor the purposes of vegetable life. 



The only substances which can with propriety 

 be called fossil manures, and which are Ibund un- 

 mixed with the remains of any organized beings, 

 are certain alkaline earths, or alkalies, and their 

 combinations. 



The only alkaline earths which have been hi- 

 therto applied in this way, are lime and magne- 

 sia. Potassa and soda, the two fixed alkalies, are 

 both used in certam of their chemical corapounds.^ 

 I shall state in succession such facts as have come 

 to my knowledge respecting each of these bodies 

 in their applications to the purposes of agriculture; 

 but 1 shall enlarge most upon the subject of lime } 

 and if I should enter into some details which may 

 be tedious and minute, I trust, my excuse will be 

 found in the importance of the inquiry ; and it is 

 one which has been greatly elucidated by late dis- 

 coveries. 



The most common form in which lime is found 

 on the surface of the earth, is in a state of com- 

 bination with carbonic acid or fixed air. If a piece 

 of limestone, or chalk, be thrown into a fluid acid, 

 there will be an effervescence. This is owing tO' 

 the escape of the carbonic acid gas. The lime 

 becomes dissolved in the liquor. 



When limestone is strongly heated, the carbo- 

 nic acid gas is expelled, and then nothing remains 

 but the pure alkali earth : in this case there is a 

 loss of weight ; and if the fire has been very high, 

 it approaches to one-half ihe weight of the stone j 

 but in common cases, limestones, if well dried be- 

 fore burning, do not lose much more than from 30 

 to 40 per cent., or from seven to eight parts out 

 of 20. 



I mentioned, in discussing the agencies of the 

 atmosphere upon vegetables, in the beginning of 

 the fifth lecture, that air always contains carbonic 

 acid gas, and that lime is precipitated from water 

 by this substance. When burnt lime is exposed 

 to the atmosphere, in a certain time it becomes 

 mild, and is the same substance as that precipitat- 

 ed from lime-water ; it is combined with carbonic 

 acid gas. Quicklime, when first made, is caustic 

 and burning to the tongue, renders Tegetable 

 blues green, and is soluble in water ; but when 

 combined with carbonic acid it loses all these 

 properties, its solubility, and its laste : it regains 

 its power of effervescing, and becomes the same 

 chemical substance as chalk or limestone. 



Very few limestones or chalks consist entirely of 

 lime and carbonic acid. The statuary marbles or 

 certain of the rhomboidal spars, are almost the 

 only pure species ; and the different properties of 

 limestones, both as manures and cements, depend 

 upon the nature of the ingredients mixed in the 

 limestone; for the true calcareous element, the 

 carbonate of lime, is uniformly the same in nature, 

 properties, and effects, and consists of one propor- 

 tion of carbonic acid 41-4, and one of lime 55. 



When a limestone does not copiously effervesce 

 in acids, and is sufficiently hard lo scratch glass, 

 it contains siliceous, and probably aluminous earth. 

 When it is deep brown or red, or strongly colored 

 of any of the shades of brown or yellow, it con- 

 tains oxide of iron. Wlien it is not sufficiently 

 hard to scratch glass, but effervesces slowly, and 

 makes the acid in which it effervesces milky, it 

 contains magnesia. And when it is black and 



« 



