98 



AGRICULTURAL CHEMISTRY. 



The mannite formed by the putrefaction 

 of beet-roots and other plants which contain 

 .sugar, contains the same number of equiva- 

 lents of carbon and hydrogen as the sugar 

 of grapes, but two atoms less of oxygen; 

 and it is highly probable that it is produced 

 from sugar of grapes, contained in those 

 plants, in precisely the same manner as in- 

 digo-blue is converted into deoxidised white 

 mdigo. 



During the putrefaction of gluten, car- 

 bonic acid and pure hydrogen gas are 

 evolved ; phosphate, acetate, caseate, and 

 laetate of ammonia being at the same time 

 produced in such quantity, that the further 

 decomposition of the gluten ceases. But 

 when the supply of water is renewed, the 

 decomposition begins again, and in addition 

 to the salts just mentioned, carbonate of am- 

 monia and a white crystalline matter re- 

 sembling mica (caseous oxide) are formed, 

 together with hydrosulphate of ammonia, 

 and a mucilaginous substance coagulable 

 by chlorine. Lactic acid is almost always 

 produced by the putrefaction of organic 

 bodies. 



We may now compare fermentation and 

 putrefaction with the decomposition which 

 organic compounds suffer under the influ- 

 ence of a high temperature. Dry distilla- 

 tion would appear to be a process of com- 

 bustion or oxidation going on in the interior 

 of a substance, in which a part of the car- 

 bon unites with all or part of the oxygen of 

 the compound, while other new compounds 

 containing a large proportion of hydrogen 

 are necessarily produced. Fermentation 

 may be considered as a process of combus- 

 tion or oxidation of a similar kind, taking 

 place in a liquid between the elements of 

 the same matter, at a very slightly elevated 

 temperature; and putrefaction as a process 

 of oxidation, in which the oxygen of all the 

 substances present comes into play. 



CHAPTER VI. 



EREMACAUSIS, OR DECAY. 



IN organic nature, besides the processes 

 of decomposition named fermentation and 

 putrefaction, another and not less striking 

 class of changes occurs, which bodies suf- 

 fer from the influence of the air. This is 

 the act of gradual combination of the com- 

 bustible elements of a body with the oxygen 

 of the air ; a slow combustion or oxidation, 

 to which we shall apply the term of ere- 

 macausis. 



The conversion r.f wood into humus, the 

 formation of acetic acid out of alcohol, ni- 

 trification, and numerous other processes, 

 are of this nature. Vegetable juices of 

 every kind, parts of animal and vegetable 

 substances, moist sawdust, blood, &c., can- 

 not be exposed to the air, without suffering 

 immediately a progressive change of colour 



I and properties, during which oxygen is ab 

 ! sorbed. These changes do not take place 

 when water is excluded, or when the sub- 

 stances are exposed to the temperature of 

 32, and it has been observed that different 

 bodies require different degrees of heat, in 

 order to effect the absorption of oxygen, 

 and, consequently, their eremacausis. The 

 property of suffering this change is pos- 

 sessed in the highest degree by substances 

 containing nitrogen. 



When vegetable juices are evaporated by 

 a. gentle heat in the air, a brown or brown- 

 ish-black substance is precipitated as a pro 

 duct of the action of oxygen upon them. 

 This substance, which appears to possess 

 similar properties from whatever juice it is 

 obtained, has received the name of extractive 

 matter; it is insoluble or very sparingly 

 soluble in water, but is dissolved with facil- 

 ity by alkalies. By the action of air on 

 solid animal or vegetable matters, a similar 

 pulverulent brown substance is formed, and 

 is known by the name of humus. 



The conditions which determine the com 

 meneement of eremacausis are of various 

 kinds. Many organic substances, particu- 

 larly such as are mixtures of several more 

 simple matters, oxidise in the air when 

 simply moistened with water; others not 

 until they are subjected to the action of al- 

 kalies ; but the greatest part of them undergo 

 this state of slow combustion or oxidation, 

 when brought in contact with other decay- 

 ing matters. 



The eremacausis of an organic matter is 

 retarded or completely arrested by all those 

 substances which prevent fermentation or 

 putrefaction. Mineral acids, salts of mer 

 cury, aromatic substances, empyreumatic 

 oils, and oil of turpentine, possess a simi- 

 lar action in this respect. The latter sub- 

 stances have the same effect on decaying 

 bodies as on phosphuretted hydrogen, the 

 spontaneous inflammability of which they 

 destroy. 



Many bodies which do not decay when 

 moistened with water, enter into eremacau- 

 sis when in contact with an alkali. Gallic 

 acid, haematin, and many other compounds, 

 may be dissolved in water and yet remain 

 unaltered ; but if the smallest quantity of a 

 free alkali is present, they acquire the pro- 

 perty of attracting oxygen, and are con- 

 verted into a brown substance like humus, 

 evolving very frequently at the same time 

 carbonic acid. (Chevreul.) 



A very remarkable kind of eremacausis 

 takes place in many vegetable substances, 

 when they are exposed to the influence of 

 air, water, and ammonia. They absorb 

 oxygen very rapidly, and form splendid 

 violet or red- coloured liquids, as in the case 

 of orcin and erythrin. They now contain 

 an azotised substance, not in the form of 

 ammonia. 



All these facts show that the action of 

 oxygen seldom affects the carbon of decav 

 ing substances, and this corresponds exactly 



