17 



TANNIC ACID, TANNIN. 



TANNIC ACID, TANNIN. 



18 



able it touches, because the ammonia is in a caustic state. If a cow 

 drop her urine in a field in a hot summer's day, all the grass it has 

 touched becomes yellow and is burned up : but if the same happen 

 in rainy weather, the spot soon becomes very green, and the grass 

 luxuriant ; because, in this case, the urine is amply diluted and its 

 caustic nature corrected. Those who live near gas-works may collect 

 the ammoniacal gas-water in a tank, and, by the addition of sulphuric 

 acid in very small quantities, they may produce a very fertilising 

 liquid, which will stimulate vegetation, and be a very good manure. 



The necessary concomitant of a tank, whether for water or manure, 

 is a water-cart, that is, a large cask put upon wheels to bring water 

 from some distance. When there are no means of bringing water in 

 pipes, a water-cart is quite indispensable. It is simply a cask placed 

 on the frame of a cart, with a plug-hole in the end or lower part, from 

 which the water may be let out by a cock, or drop on a flat board or 

 into a bucket with holes, so as to spread it about. The plug-hole is 

 shut by a valve inside, which can be opened by means of a string, the 

 pressure of the liquid keeping it close to the plug-hole. 



Many of the artificial manures would make excellent liquids by 

 merely mixing them up with water in a tank, and allowing a certain 

 degree of fermentation to take place. Thus nothing is lost, and all 

 volatile substances are taken up by the water. The soluble portions 

 are dissolved and the earthy matters diffused, so as to be more equally 

 spread over the land. 



When a farm-yard is situated on a hill, and there are fields or 

 pastures on a lower level, at no great distance from it, the liquid from 

 the tank may be conducted by channels lined with clay, having small 

 sluices to direct the streams to any particular field. It may thus be 

 made to irrigate temporarily a considerable surface, which it will 

 greatly enrich. It may be led into the common furrows between the 

 lands or btitches in ploughed land, and allowed to soak in them, 

 and then it can be spread with the earth of the furrow, by means of 

 broad shovels, over the growing crops, and will greatly invigorate 

 them. 



Hitherto the experience in this country of liquid-manure tanks is of 

 limited extent, but the general impression is growing, that by covered 

 yards and box-feeding the litter may so absorb all the urine and excre- 

 ment of the animals, that tanks will be unnecessary. 



TANNIC ACID, TANNIN. One or other of these bodies is 

 found, to a greater or less extent, in most vegetable substances. The 

 name tannin is derived from the fact that it is the only active constitu- 

 ent in the various barks, &c., used in the familiar operation of making 

 leather, or tanning. 



Tannin is an acid body ; and inasmuch as researches upon the tannin 

 obtained from various sources have proved that it is not in all cases 

 identical, but that several modifications exist, the names gaUotannic 

 acid (from nut-galls), cafotannic acid (from coffee), tjuinotannic acid 

 (from cinchona bark), quercitannic acid (from oak-bark), &c., have been 

 introduced. 



Tannic acid is a powerful astringent, and hence has long been used 

 in nimliciue. For this purpose it is always extracted from nut-galls. 

 The galls are reduced to coarse powder, and digested in a percolator 

 with ether which has been previously mixed and shaken with water. 

 In tliu lower part of the vessel two strata of liquid appear ; the heavier 

 is a strong solution of tannic acid, by evaporating which, the acid is 

 obtained, as a colourless or slightly yellowish friable mass, which does 

 not crystallise, but somewhat resembles dried gum. 



The gaUotannic acid thug obtained is readily soluble in water : the 

 solution has an astringent but not a bitter taste : it reddens vegetable 

 bluex, and decomposes alkaline carbonates with effervescence ; weak 

 aluohol dissolves it, but ether only slightly. When the aqueous solu- 

 tion is exposed to the air, especially if the temperature be high, oxygen 

 gas is absorbed, and an equal volume of carbonic acid gas evolved, 

 while the gaUotannic acid is converted into gallic and ellagic acid. 

 GaUotannic acid precipitates gelatin from solution ; the compound has 

 been called Ininmi/iliiiiii, and when the acid is in excess a viscid elastic 

 mass is formed, which contains about half its weight of gaUotannic 

 acid. W'hen the liquid from which the gelatin is precipitated is heated 

 to ebullition, the tannogelatin is re-dissolved. GaUotannic acid also 

 precipitates albumen and starch. Boiled with dilute sulphuric or 

 hydrochloric acids, gaUotannic acid splits up into gallic acid and 

 glucose. 



When dried at 212 gaUotannic acid consists of C 4 ,H M O M . 



GaUotannic acid combines with the alkalies to form salts, which are 

 called ga/lotannatft, and it precipitates most metallic oxides and organic 

 banes from solution. The salts of protoxide of iron suffer no change 

 when a solution of gaUotannic acid is added to them ; but by exposure 

 to the air a deep bluish-black precipitate is formed. GaUotannate of 

 peroxide of iron, formed by the action of the acid on a persalt of the 

 metal, U the basis of writing-ink, and is a black pulverulent precipitate. 

 ''mtc or tanningeaamic acid (C 14 H,NO, + 3 Aq) is a product of the 

 action of ammonia on gaUotannic acid. It crystallises from alcohol in 

 beautiful rectangular plates. 



Taiim/melanic acid is a dark ulmin-like substance formed when 

 gaUotannic acid is boiled with a concentrated solution of potash in a 

 vessel open to the air. If the potash be dilute, a portion of the acid is 

 oxidised to tannoj-ylic acid. The constitution of these acids has not 

 been satisfactorily ascertained. 



ABTS ASD CI. DIV. VOL. VIN. 



Sumach-tannic acid, from various species of sumach, is identical with 

 gaUotannic acid. 



Cachoutannic acid or mimotannic acid. Obtained from the well-known 

 astringent substances KINO and CATECHU by the displacement process 

 previously described. It differs from gaUotannic acid in not giving a 

 precipitate with solution of tartar emetic, and in giving with persalts 

 of iron a grayish-green precipitate. Moreover, it does not yield pyro- 

 gallic acid when heated. Its composition is said to be C 3a H, 8 10 . In 

 other respects it resembles gaUotannic acid. 



Tanninyenic or catechucic acid, called also catechin (C 10 H 18 1() ?), is 

 another tannic acid contained in catechu. It is part of the insoluble 

 portion which is left on digesting catechu in cold water. It may be 

 dissolved in boiling water, and decolorised by animal charcoal : on 

 cooling, it deposits in colourless granular crystals. It is tolerably 

 soluble in alcohol ; less so in ether. Heated to 422 Fahr., it fuses, and 

 at a higher temperature is decomposed, yielding pyrocatechin or oxy- 

 phenie acid (C,,,H 6 4 ). Dilute acids dissolve it; concentrated acids 

 decompose it ; hot nitric acid converts it into oxalic acid. It does not 

 form definite compounds with bases ; gives a deep green colour to per- 

 salts of iron, but precipitates neither lime-water, baryta-water, tartar- 

 emetic, starch, gelatin, or the alkaloids. 



RufocaUchucic acid or rubinic acid is a red, amorphous, flocculent 

 precipitate, slowly deposited from a solution of tauningenic acid in an 

 alkaline carbonate. It forms red slightly soluble salts with bases. 



Japonic acid is a black substance formed on exposing to the air a 

 solution of tanningenic acid in caustic potash. It is insoluble in cold 

 water, and gives black precipitates with most of the metals. 



Caffutanuic, cafeic, or chloroginic acid (C 70 H M 3t ?), occurs in coffee 

 berries as a double salt of potash and caffeine, and combined also with 

 lime and magnesia. It may be precipitated by subacetate of lead from 

 an alcoholic infusion to which water has been added to separate 

 resinous matter. The lead precipitate suspended in water and treated 

 with sulphuretted hydrogen, and the nitrate evaporated, yields a semi- 

 crystalline mass of caffotannic acid. It is very soluble in water, less so 

 in alcohol, has an astringent taste, and strongly reddens litmus-paper. 

 By heat it gives oxyphenic acid and an odour of burnt coffee ; and by 

 distillation with peroxide of manganese and sulphuric acid, yields 

 kinone. It does not act upon ferrous salts, but to the ferric salts a 

 green colour is imparted. It does not precipitate tartar emetic or 

 gelatine, but throws down quinine and cinchonine from solutions. 

 The cafotannate have been but little studied. If the above formula 

 be correct, caffotannic acid is obviously a homologue of gaUotannic 

 acid, the difference being eight equivalents of C a H ? . 



Viridic acid (C SS H U 1( , ?) is a product of the oxidation of caffotannic 

 acid in the presence of ammonia. It is precipitable by subacetate of 

 lead, and gives deep green solutions with the alkalies. 



Morintannic acid, from yellow wood or fustic (Morua tinctoria). This 

 acid often forms considerable deposits in the logs of fustic, and after 

 being purified by crystallisation from water is obtained in minute 

 prisms. It has a sweetish and yet astringent taste ; is soluble in 

 alcohol, ether, and wood spirit, but insoluble in turpentine and the 

 fixed oUs. By distillation it yields phenic and oxyphenic acids and 

 much charcoal. The morintannatei have not received much attention. 

 The solution of the acid in potash absorbs oxygen from the air, 

 blackens, and muroxylie acid is probably formed. 



Rufimmic acid is deposited in crystalline grains on exposing to the 

 air a solution of morintannic acid in sulphuric acid ; or on boiling the 

 same acid with dilute hydrochloric acid. When dry it forms a deep 

 red amorphous powder, very soluble in alcohol, less so in water, and 

 only sUghtly so in ether. It is very soluble in a weak solution of 

 ammonia, and the liquid has a dark purplish colour. In composition 

 it differs but slightly from morintannic acid, but both bodies require 

 farther investigation. 



Marie acid, or morin (C,,H, 4 O ls -l-2Aq.), as a Ume salt, is deposited 

 on cooling an infusion of fustic. Liberated by oxalic acid in a boiling 

 alcoholic solution and precipitated by water, it occurs as a white crys- 

 talline powder that becomes slightly coloured on exposure to the air. 

 It is almost insoluble in cold water, only slightly soluble in boiling 

 water, and very soluble in alcohol or ether. 



Quercitannic acid. This is the variety of tannic acid contained in 

 oak bark. According to Stenhouse it differs considerably from that of 

 oak galls (gaUotannic acid). It cannot be made to yield gallic acid, nor 

 does it give pyrogallic acid by dry distillation. In other respects it 

 resembles gaUotannic acid. 



The tannic acid (Mteic acid) contained in black tea (Thca, Ixthea) ap- 

 pears to be identical with that of oak bark. 



Cinchotannic, kino- or quino-tannic acid, occurs, along with kinic acid, 

 combined with alkaloids in the cinchona barks. It resembles gaUo- 

 tannic acid in precipitating gelatin, starch, and albumen from their 

 solutions ; with tartar-emetic it gives a grayish-yellow precipitate, and 

 colours persalts of iron green. Its solution absorbs oxygen from the 

 air, especially if it be alkaUne, and a deep red coloured body termed 

 red cinctutne is formed. By dry distiUation the latter body furnishes 

 pyrogallic acid. 



Other tannic acidt. Astringent principles, termed tannic acids, have 

 been found in plants other than those above described. The following 

 are the names and sources of these acids, but their individuality has 

 yet to be established. Aupcrlannic acid, from the Agenda odnmta, or 



