m 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Mat, 



The second group, having excess of hydrogen, consists of resins, oils, fat, 

 &c. They are present in nearly all our food. The greater number of them 

 are found to consist of two substances, termed by chemists, elaine and 

 stearine, the latter being the solid principle. In the solid fats these may be 

 separated by pressure, as in the manufacture of linseed, cocoa nut, olive, and 

 other oils. There is a dispute at present in the scientific world, whether 

 animals have or have not the power of forming fat in their system from food 

 which does not contain It, but all agree that when present in the food the 

 animal can treasure it up in certain parts of the body. 



The third group, containing oxygen in excess, embraces, with one exception, 

 the whole of the acids in vegetables which have no nitrogen ; this exception, 

 which is acetic acid or the acid of vinegar, is never obtained except by de- 

 composition. These acids are abundantly secreted in some plants, and are 

 also said to be excreted by the roots of most plants. Wood is converted partly 

 into acetic acid when it is distilled at a strong heat, and in this manner most 

 of the vinegar used at table is obtained. Sugar is also converted into vinegar 

 very readily ; a little vinegar added to a large quantity of sugar and water, 

 causes the whole of the sugar to disappear, and acetic acid is found in its 

 stead. Tartaric is one of the commonest vegetable acids, being present in 

 nearly all sour-leaved plants. It obtains its name from being the acid in the 

 tartar of wine. When tartaric acid is neutralized by potash, it forms a 

 very soluble substance, but when the acid is in excess, the compound is 

 \rery insoluble, and is precipitated as cream of tartar, or bitarlrate of 

 potash. It is from this deposit taking place more largely in the juice of the 

 grape which renders it so fit to make the best wine; other juices, retaining 

 this acid yi solution, produce consequently sour wines. In forming these 

 acids, the plant is absorbing oxygen from the air instead of yielding it, and 

 in the growth of such fruits as lemons, the amount absorbed must be consider- 

 able. 



Lecture IX. 

 The fourth section of proximate principles, or those containing nitrogen- 

 are considered as being the most essential to animal life, they going to form 

 new flesh in the animal, whilst all the other principles are supposed to be 

 consumed during respiration, principally in order to maintain the heat of the 

 body. When the gum, starch and sugar were washed out from wheat flour, 

 an adhesive fibrous substance was left called gluten. This contains all ihe 

 nitrogenous substances in the flour, not being a simple principle, but a 

 mixture of three or four ; one is like cheese, one like white of egg, but all 

 contain nitrogen. They are characterised by their action towards various 

 solvents, but as they are very similar in composition, they are not worth 

 separating, when considered as food for animals. It has been lately shown 

 by Mulder, that when deprived of extraneous salts, and of a little sulphur 

 and phosphorus, they exactly resemble the nitrogenous principles of ani- 

 mals, that, in fact, they have exactly the same composition, whether derived 

 from animal or vegetable, and are only modifications of one principle, to 

 which he has given the name of proteine. They may therefore be represented 

 as follows : — 

 Albumine 'k 



Case'ine f t-'^rbon 84 + Hydrogen 36 + Nitrogen 6 + Oxygen 15. 

 Glutine ) 

 It is essential that an exact mode of ascertaining the quantity of nitrogen 

 present in a substance should be known ; and there has lately been proposed 

 by Will and Varrentrap, a very delicate method of .effecting this. When an 

 organic substance is mixed with caustic potash or soda, and lime, and then 

 heated, the whole of the nitrogen present is driven oft' as ammonia, which may 

 be ascertained by its smell, by its action on moistened litmus paper, and by 

 the fumes formed by holding a rod dipped in muriatic acid over it. If this 

 is collected by being passed into muriatic acid, sal-ammoniac, or chloride of 

 ammonium is formed ; w hen to this is added a solution of platinum, a copious 

 brown precipitate is formed, consisting of the ammonio-bichloride of plati- 

 num. This dried and weighed, will indicate the quantity of ammonia or 

 nitrogen evolved from the heated organic substance, 225 grains of it con- 

 taining 17 of ammonia, or 14 of nitrogen. Or, it may be decomposed by a 

 red heat, and 14 grains of nitrogen reckoned for every 99 grains of platinum 

 that is lelt, as its following composition will prove : — 

 Ammonio-bichloride of platinum, 

 fchUine : : : 72} l^lBl-chlorideofplatinum. 



C&T : : : ,1} ^T^y^rocUonccM. 



3 Hydrogen . . . 3 X 



Nitrogen . . . 14 j 



The value of various substances as food for animals being considered to be 

 according to the quantity of nitrogen they contain, lists have been drawn up 

 to show their comparative richness in nitrogen. In the following list, the 

 numbers attached show the quantity of the various substances that is neces- 

 sary to yield an equal amourt of nitrogen :— 



17 Ammonia. 



Hay . 

 Clover hay 

 Vetch hay 

 Wheat straw 

 Barley straw 

 Oat straw 

 It follows, as a necessary consequence, that when animals are fed on sub- 

 stances poor in nitrogen, they must eat more of such food than would be re- 

 quisite were they fed on richer food. Thus vegetable feeders eat a greater 

 quantity than do animal feeders ; men fed on fish, potatoes; or rice, require to 

 eat more in proportion. But neutral substances, also, such as gum, sugar, 

 Sic, are required for the sustenance of life, and consequently we find in milk, 

 the liquid prepared by nature for the food of the young animal, a proper ad- 

 mixture of all these requisites. In lOCO parts of milk are found, according to 

 analysis, 



Caseine 45 to 90 



Sugar 36 „ 50 



Butter 27 „ 35 



Phosphate of lime and other salts , . 9 „ 10 

 Water 883 „ 815 



1000 1000 



The various processes of decay, such as fermentation, putrefaction, and 

 eremacausis, fthe latter term being the one now fashionable to describe the 

 slow decay of woody substances) may all be considered as the return of com- 

 plex substances to those more simple in composition. The fibrin, &c., consist 

 of high numbers, but in putrefaction they are reduced to substances with luw 

 numbers, passing off as carbonic acid, water, and abundance of ammonia. In 

 the vinous fermentation, the alcohol is a tertiary compound, carbonic acid a 

 binary one. In eremacausis, all the compounds are given oft' as carbonic acid, 

 water, and a little ammonia. Thus they all pass into air. 



To ascertain how the proximate elements are produced and changed in 

 plants, the germination of the seed must be watched. Although there is an 

 infinite variety in the appearance of seeds, and consequently they might be 

 supposed to difl'er a great deal, yet all agree in containing but two essential 

 parts, the germ, and food for it to consume before it has put forth roots to 

 gather it for itself. In the cocoa nut, these are covered by a outer fibrous 

 coat, then a hard woody one, then the food or albumen of the seed, as it is 

 termed, buried in which, at the soft end of the husk, is the embryo. It is 

 similar to this in the smallest seed. In the chesnut, when the husk is re- 

 moved, a mealy matter is seen, in the small end of which is the germ. When 

 the germ grows, great changes take place in the seed, for which water, air, 

 and a certain temperature are requisite, but no light, it being detrimental to 

 a growing seed. If one of these conditions is absent, the seed will not grow. 

 If they are present, provided the seed has not lost its vitality, it is sure to 

 grow. Seeds differ very much in their power of retaining vitality, some re- 

 maining dormant in the soil for years, nut germinating until the soil should 

 by chance be turned up, they either wanting air or heat. Clayey soils, by 

 enveloping the seed, prevent the air from getting to it. For want of moisture 

 seeds lie dormant but still not dead, as is proved by a crop now growing from 

 seed taken from Egyptian tombs. With the requisite circumstances, seeds 

 swell, soften, and burst their membranes, the germ puts forth its radicle, 

 which pierces the earth and sends out rootlets, after \\ hich the stem shoots up, 

 and forms branches. At first the seed, feeding on the carbonaceous matter 

 stored up, abstracts oxygen from the air, and evolves carbonic acid, but its 

 province afterwards, when it has formed roots and leaves, is to decompose the 

 carbonic acid of the air and to liberate oxygen. The roots of plants are said 

 to throw out acetic acid; when they have been grown in powdered marble, 

 acetate of lime has been found. Liebig and others insist much on this point, 

 considering that it is by this means that plants render insoluble substances 

 soluble. During germination, a portion of the gum and starch in the seed is 

 converted into sugar, which is called the process of saccharification. In 

 growing plants a substance called diastase is formed, which has the remark- 

 able property of being able to convert many times its weight of starch or gum 

 into sugar, and it is in this manner that seeds whilst growing become so sweet. 

 This is seen beautifully in the process of malting, which consists in allowing 

 the barley to grow until its maximum of sugar is formed, which is just when 

 the plumule begins to show, and then stopping it by drying. If the diastase 

 had been previously washed out with water it would have been spoilt for malt, 

 as saccharification would not have taken place. For beer making, the malt is 

 bruised in hot water, and the action of the diastase goes on, the mucilage and 

 starch is converted into sugar, and this again is decomposed into alcohol and 

 carbonic acid. 



When the young plant has exhausted the storehouse nature has provided it 

 with, it is strong enough to derive its food by its roots and leaves, until which 

 time no true wood is formed. The stem of a plant may be seen to consist of 

 several parts, the centre portion, or pith, becoming obliterated as the plant 

 grows ! the wood is of two kinds, the old or heart wood, and the new w ood or 

 alburnum; in like manner the bark is of two kinds, the newer being termed 

 the liber. The bark is connected viith the pith by layers running from it, 



