THE TROPICAL AGRICULTURIST. 



[Aprit, I, 1884. 



Hj^ents alone seem to operata ; but in the animal system 

 those agents are made subservient to a superior prin- 

 ciple. 



Agricultural chemistry has for its objects all the changes 

 in the arrau-jements of matter connected with the growth 

 and nourishment of plants; the comparative values of 

 their produce as food ; the constitution of soils ; the manner 

 iu which lauds are enriched by manure, or rendered fertile 

 by the ditft-rent processes of cultivation. Inquiries of such 

 a nature cannot but be interesting and important both ■ 

 to the theoritical agriculturist and to the practical farmer. 

 To the first, they are necessary in suppljdng most of the 

 fundamenlal principles on which the theory depends. To 

 the second, tliey are useful in affording simple and easy 

 experiments for directing his labors, and for enabling him 

 to pursue a certain and systematic plan of improvement. 



The presence of a growing plant, of the root of a seed, 

 where life is, impresses on the soil, both on the organic 

 and inorganic elements, power to enter into new arrange- 

 ments. The soil, then, is not external to the plants ; 

 so far as life is concerned, it is as much internal as if 

 the plant had a mouth and a stomacb,through, and into 

 which the soil might be fed. 



What are the principle simple chemicals that influence the 

 growth of vegetables ? 



They are carbon, oxygen, hydrogen and nitrogen. The 

 other substances of plants, it will be seen, are compounded 

 of two or more simple elements. 



There is no reason why the agriculturist should not be 

 as familiar with the names and properties of carbon, oxygen, 

 hydrogen and nitrogen as he is with those of coals, hme 

 and salt. Being familiar with the primary elements, he 

 will the more readily comprehend the functions of vege- 

 tables, and the conditions favourable to their development. 

 Who, without any formal scientific instruction, is not familiar 

 with the names of u'on, sulphur, potash, soda and lime? 

 No ono ; for they are of every day occurrence. And who 

 does not know that coal is carbon ? And who has never 

 heard that oxygen and nitrogen form the air we breathe; 

 or that water is composed of oxygen and hydrogen? 



With alumina or alum all are familiar. Silex or silicia 

 is but the name t>f portions of hard stones. Most persons, 

 too, are no strangers to what is called ammonia, which 

 is a combination of nitrogen and hydrogen, is sometimes 

 called sal volatile, and is what gives the sharp smell iu 

 the smelling-boltlt;,or the manure heap. It is the ammonia 

 i.i manure which is so efficacious in agriculture. And if 

 the reader is less familial- with the name of chlorine, it 

 is easy to give him some hints of it. This is the substance 

 used in bleaching cotton goods, and on opening them the 

 smell is very pungent for a long time. And what is still 

 more iu point, chlorine united with soda makes our com- 

 mon salt ; or, if united with ammonia, the product is what is 

 called in the shops sal ammoniac. The circumstance that 

 chlorine is a constituent of common salt is in itself suffi- 

 cient to give it an interest in impressing it on the me- 

 mory of every individual. 



Chlorine is important also from bsiug used to disinfect 

 the air when impregnated with foul vapors, as in the case 

 of cholera and other diseases. Here, then, is nearly the 

 whole catalogue of these obnoxious terms, save manganese, 

 which is simply a dark-coloured metal, u.'=;ed in the manu- 

 facture of glass as well as in agriculture. 

 What is " an element ? " 



A body that is constituted of one kind of matter only, I 

 is called an element. One that is composed to two ele- 

 ments, isa compound. 



If a body consists of three elements, it is called a ter- 

 nary compound ; if of four a quarternary compound. Bi- 

 nary implies two-fold ; teruary, three-fold, andiquar ternary 

 four-fold. 



Iron, being composed of one kind of matter, is an ele- 

 ment ; the rust of iron is a compound, being formed of 

 oxygen and iron. Put a little drop of water upon a piece 

 of bright iron ; after a short time, wipe it away, and there 

 will remain a spot of rust. The oxygen of the water, or a 

 part of it, will have combined with portions of the iron, 

 and fornu'd an rxide of iron, a binary compound, or com- 

 pound of two elements. Water is composed of two ele- 

 ments ; Eijsom salts of three ; alum of four, and so on. 



We must distinguish between a compound and a mixture. 

 When two substances combine of their own accord, as if 



self-moved, the result is a compound. If they are only put 

 together by mechanical force, it is a mixture. In the first 

 case, the properties of the ingredients are entirely changed ; 

 in the last, they remain unaltered. Thus, if you bring 

 chlorine and sodium together, a substance totally unhke 

 either is produced — from two virulent poisons, a wholesome 

 condiment, common salt, is formed : this is a compound. 

 But if you put water with milk, no new substance is formed 

 —the properties of the ingredients remain mialtered ; they 

 are water and milk still, and nothing more : this is a mere 

 mixture. 



What is carbon ? 



Carbon is a chemical element, abounding in nature, the 

 most familiar form of which is charcoal. How large a 

 proportion of vegetables consists of this substance may be 

 ascertained by charring a piece of wood. 



When wood is burnt with a smothered flame, the volatile 

 parts are driven otf by heat, and there remains behind a 

 substance exhibiting the exact form, and even the several 

 layers of the original wood. This process is denominated 

 charring, and the substance obtained charcoal. As it is the 

 woody fibre alone which resists the action of the heat, while 

 the other parts of the substance are dispersed, it is plain 

 that charcoal must be the residium of woody fibre, and 

 that the quantity of the one must depend upon the quantity 

 of the other, if they are not to be considered actualiy the 

 same. Charcoal may be obtained from almost all the parts 

 of plants, whether solid or fluid. 



The properties of charcoal are, insolubility in water, of 

 which however, it absorbs a portion when newly made, as 

 also of atmospheric air. It is incai^able of putrefaction. It 

 is notaltt-red by the most violent heat that can be applied, 

 if all air and moisture are excluded. But, burnt iu air, 

 it conabines with the oxygen of the atmosphere, forming 

 carbonic acid gas ; and it is important to bear in mind that 

 this gas is one of the natural constituents of the atmos- 

 phere, by which plants are surrounded. 



What is oxygen ? 



Oxygen is an element known only in the state of a gas, 

 or in an iir-like condition. It is void of color, taste and 

 smell, and therefore cannot be distinguished from com- 

 mon air. It exists in the atmosphere, in water, and in min- 

 erals, and is necessary to the life of both plants and animals. 



What is hydrogen ? 



Hydrogen is also known to us only in the state of gas, 

 and wheu perfectly pure is scarcely distinguishable from 

 common air, being without color or taste, and posses-siug but 

 Uttle smell. Although we can easily obtain it as a gas, 

 it does not usually exist as such, but it combines with all 

 animal and vegetable substances, abounds in water, and is 

 found largely iu coal, but is not found in any other of 

 the large miueral masses. 



What is nitrogen ? 



Nitrogen, also, is known to us only in the form of gas. 

 It is without color, taste or smell. It is found most 

 abundantly in the atmosphere ; and forms apart of many 

 animal and some vegetable substances. 



Such are the simple elementary bodies of which the or- 

 ganic, or destructible part, of vegetable substances is formed. 

 With one exception, they are known to us only in the form 

 of gases ; and yet. out of these gases much of the solid parts 

 of animals and ot plants are made up. When alone at the 

 ordinary temperature of the atmosphere, they form invisible 

 kiuds of air; when united, they constitute those various 

 forms of vegetable matter which it is the aim and end of 

 the art of culture to raise with rapidity, with certainty, and 

 in abundance. How dithcalt to understand are the intricate 

 processes by which nature works up these rare materials 

 into her many beautiful productions ; yet how interesting it 

 must be to know her ways — how useful even partially to 

 find them out. — Leader. 



THE EUCALYPTUS. 



TO THE EDITOR OF THE "SYDNEY WAIL." 



Sir, — In the Dec- mber number of the Medical Gazette 

 I was pleased to notice an article on tlic above .subject 

 from the pen of Harou Mueller. It is a subject that I 

 have long taken a dcpp interest in, and therefore, on the 

 present occasion, I crave yoiu' indulgence while I offer a 

 few remarks on the mattir. I have no ilesire in the 

 sequel to say one word with the view of detracting iu 



