EARTHS. 



EARTHS. 



ing table exhibits the results of these trials, 

 supposing the original weight of each salt to 

 have been 100. Each solution contained one 

 hundredth part of its weight of each salt 



Proportioni 



I C Glauber salt - - - - 117 



v r< 1 Common salt .... 22'0 



C Glauber salt - 6'0 



2. 1 Common salt - lO'O 



(.Acetate of lime] - 



On examining the plants the salts absorbed 

 were found in them unaltered." (Chemistry, 

 vol. iv. p. 325.) In these experiments the cul- 

 tivator will observe that the plants (which were 

 Spotted Persicaria (Polygomtm Pcrsicaria') and 

 the Bur-marigold (Eidens tripurlita), with their 

 roots attached) absorbed the common salt with 

 avidity, but that they rejected entirely the ace- 

 tate of lime. The earths are, in all probability, 

 always imbibed by the plant in a state of solu- 

 tion ; we know, in fact, that both lime and 

 silica are, to a certain extent, soluble in water, 

 and alumina is also very probably absorbed as 

 a component of some of the soluble salts which 

 contain this earth. 



The part which the earth fulfils in the sup- 

 port of plants early attracted the attention of 

 philosophers. The earthy ashes produced by 

 the combustion of vegetable substances must 

 have very soon indicated to mankind the real 

 truth of the case, that there were certain solid 

 substances found in vegetables which they 

 could only derive from the earth they tenanted. 

 That the soil furnished its earthy matter to the 

 plant was, therefore, the natural conclusion of 

 some of the Greek philosophers ; and although 

 their observations in this way were commonly 

 very loose, and always general, yet when they 

 decided, which they did with all gravity, that 

 earth, air, fire, and water composed every thing 

 on the'earth, the vegetable world was of course 

 included in the list ; they still, however, thought 

 that the chief use of the earth to plants con- 

 sisted in keeping them upright, and furnishing 

 them with a sufficient supply of moisture. 



When the ancient naturalists came to the 

 conclusion that the whole earth was composed 

 of four elements, they founded their decision 

 upon certain rude observations ; but they did 

 not stop there, they proceeded to confuse theni- 

 selves by various incomprehensible or delu- 

 sive phrases, such as more modern observers 

 have too often imitated. Fire they regarded as 

 the active principle of the universe, the source 

 of both animal and vegetable life, the cause 

 of renovation and decay. Earth they consi- 

 dered as the principle of fixity, of hardness, 

 and of solidity. These rude, though sagacious 

 observations, the early chemists, and then the 

 alchemists, strongly confirmed by the mode in 

 which they analyzed vegetable substances. 

 They had only one mode of effecting this, that 

 of subjecting them in a retort to dry or de- 

 structive distillation. By this mode the results j 

 are almost always the same ; first the water 

 of the plant comes over ; then a volume of 

 carburetted hydrogen and carbonic acid gases 

 is driven off; and finally a quantity of earthy i 

 matters, mixed with various salts and potash 

 remains at the bottom of the retort. We need , 

 hardly feel surprised, therefore, that after such | 

 428 



an analysis, the chemists of old readily agreed 

 with the naturalists that earth, air, and water, 

 alone formed the vegetable world. 



Evelyn, in 1674, wrote a work upon earth, 

 in which he lauded its powers with much en- 

 thusiasm. " What shall I say," he exclaims, 

 " Quid Divinum 1 the original of all fecundity ; 

 nor can I say less, since there was nor sacri- 

 fice nor discourse without it." And in another 

 place he says (for Evelyn was exceedingly 

 credulous), "Whatever then it be, which the 

 earth contributes, or whether it contains uni- 

 versally a seminal virtue, so specified by the 

 air, influences, and the genius of the climate, 

 as to make that a cinnamon tree in Ceylon 

 which is but a bay in England, is past my skill 

 to determine; but it is to be observed with no 

 little wonder, what M. Bernier in his history of 

 the empire of the Mogul affirms to, as of a 

 mountain there, which being on one side of it 

 intolerably hot produces Indian plants, and on 

 the other as intemperately cold, European and 

 vulgar plants." There is much valuable mat- 

 ter, however, in The Terra of Evelyn, whose 

 modesty enhanced his great merits. Thus, in 

 conclusion, he told his Fellows of the Royal 

 Society, to whom his valuable essay was ad- 

 dressed, that it was merely " a dull discourse 

 of earth, mould, and soil." 



Fitzherbert, the earliest English writer upon 

 agriculture (1532), did not pay any attention 

 to earths, beyond the usual necessary routine 

 of the farm; he confined himself entirely to 

 practical details : not a trace of any thing like 

 scientific inquiry is to be found in his Boke of 

 Husbandrye. John Worlidge, who published 

 his System of Agriculture in 1669, thought it ne- 

 cessary, as 'he professed to "unveil the mystery 

 of agriculture," to give the cultivator an expla- 

 natory chapter on the food of plants, in what 

 he called "a plain and familiar method," and 

 this he did in the true jargon of the alchemists; 

 for the age of "the transmuters" was not yet 

 over when Worlidge wrote. He gave, there- 

 fore, the husbandmen of those days a disserta- 

 tion upon "the universal spirit, or spirit of 

 mercury, the universal sulphur, and the uni- 

 versal salt;" but still, after all, he thought that 

 the earth was the true food of plants, and that 

 all the operations of the husbandman only 

 tended to enable the roots of the plant to take 

 up more earthy matter, and he devotes a chap- 

 ter of his book to the " Soyls and Manures 

 taken from the Earth." But his ideas, like those 

 of the alchemists, were usually a mixture .of 

 common sense and absurdity, too closely united 

 to be always readily distinguishable by the 

 good sense of the cultivator. 



Jethro Tull, who wrote between 1730 and 

 1740, considered earth to be the sole food of 

 plants. "Too much nitre," he tells us (p. 13, 

 of his valuable Book on Husbandry), "cor- 

 rodes a plant, too much water drowns it, too 

 much air dries the roots of it, too much heat 

 burns it ; but too much earth a plant can never / 

 have, unless it be therein wholly buried: too 

 much earth or too fine can never possibly be 

 given to their roots, for they never receive so 

 much of it as to surfeit the plant." And again, 

 he tells us in another place, "That which nou- 

 rishes and augments a plant is the true food 





