, TEA, ETC.] 



CHEMISTRY. 



351 



which, together with tanno-caffeio acid, are united witl: 

 potash into a so-called double salt. Tanno-caffoic acid, 

 wheu roasted, develops the agreeable smell of coffee. 



Not only the same basis, but also two similar organic 

 acids one contained in tea, the other in coffee in- 

 crease the conformity between the leaves of the former 

 and the beans of the latter. 



Legumin, cellulose, gum, sugar, citric acid, in addi- 

 tion to oleine and to the peculiar palm- fat, which derives 

 its name from being found in the fruit of several species 

 of palms, accompany the organic acids and the thein 

 of the coffee-beans. 



But the tea-leaves, apart from the basis and the acids, 

 are composed of albumen, cellulose, gum, and wax, 

 the green pigment of the plant, and the volatile oil of 

 tea. This peculiar oil is the principal source of the 

 aroma of tea, by which, in spite of the conformity be- 

 tween tea and coffee, it essentially differs from the 

 latter. 



The inorganic constituents of tea and coffee are, more- 

 over, different. While in coffee, chlorine, phosphoric 

 and sulphuric acids are combined with potash, lime, 

 magnesia, and oxide of iron ; tea contains another in- 

 organic acid besides, consisting of manganese and a 

 large proportion of oxygen. 



In the kernels of cocoa, of which chocolate is pre- 

 1, there are to be found, besides the cocoa-prin- 

 , stoarinc and oleino, cellulose, gum, and starch, a 

 miring matter, and a small proportion of water, 

 ry, so commonly used as a substitute or accom- 

 paniment of coffee, contains neither caffein nor any 

 other peculiar constituent of the latter. No albuminous 

 substance cvsr has, up to this time, been found in 

 chicory. As albumen is not wholly wanting in any 

 vegetable product, it must be present in chicory, though 

 in a very small quantity. But the constituents of fat 

 arc represented in a larger proportion ; for in addition 

 to cellulose, sugar, and gum, it contains a pretty con- 

 siderable quantity of a substance of the same composi- 

 tion as starch, which, by simply boiling in water, is 

 transformed into sugar. Chloride of sodium, a c-nn- 

 pound of chlorine with ammonia (the so-called sal- 

 ammoniac), sulphate and nitrate of potash, are its in- 

 organic constituents. 



As yet, therefore, no great importance as a nutriment 

 can be attributed to chicory, nor any similarity with 

 coffee. Unless a peculiar organic substance contained 

 in it, but not yet exactly investigated, shall at a future 

 time be proved to be peculiarly valuable, the infusion 

 of chicory possesses no advantage over sugared water, 

 to which a brown colour and bitter taste have been im- 

 parted ; but we do not understand this bitter substance. 

 Whilst, then, chicory cannot, on scientific grounds, be 

 made out to be a true substitute for coffee, it has, on 

 the other hand, been too partially investigated to justify 

 on absolute condemnation. 



7-. Preparation of Teas. Roasted coffee differs from 

 raw by its lighter weight and greater bulk. Several 

 empyreumatic substances, produced by roasting, occa- 

 sion the reddish or dark-brown colour ; and the tanno- 

 calluic acid, altered by roasting, produces the aroma ; the 

 ingar loses a part of its amount of hydrogen and o\\ 

 and is thus decomposed into burnt sugar or caramel. 

 In the infusion, the caffein and the acids, the gum 

 and caramel, the molted fat and the salts, with leguuiin 

 in a very slight proportion, are to be found. 



Between green and black tea, erroneously so often 

 supposed to be produced by different plants, a similar 

 difference exists to that between raw and roasted coffee. 

 The leaves are turned black by being dried at a higher 

 mature than that to whiuh the green tea has been 

 subjected. The latter is first brought into a withered 

 condition by vapour, and then dried in iron kettles; 

 while black tea is prepared by heating over an open tire. 

 As heat exercises a decomposing action, black contains 

 loss tea-oil, less tannic acid, and less green colouring 

 matter than green tea. By the process of drying, how- 

 ever, a dark product of decomposition is formed, few 

 traces of which are found in green tea, but a consider- 



able quantity in black. In China, tea is frequently 

 coloured with curcunie, and indigo or Prussian blue. 



By the effect of the open fire, in black tea the albumen 

 is more completely coagulated than in green ; by this 

 coagulation the tea-oil becomes disengaged. Partly from 

 this cause the black tea has lost a greater proportion of 

 its tea-oil than green ; and for the same reason, tea pos- 

 sesses more flavour if infused with perfectly boiling- 

 water, which coagulates all the soluble albumen, and 

 therefore dissolves the tea-oil with greater ease. But 

 the tannate of thein, also, is only sufficiently extracted 

 by boiling- water : this compound is even separated at a 

 low temperature ; and honce the turbid appearance of a 

 well-prepared infusion of tea when cooling, wliich every- 

 body knows who has ever taken his tea out of a tumbler, 

 as the Russians generally do. Thein and tea-oil, how- 

 ever, are the most important constituents of tea ; boiling- 

 water is therefore an indispensable condition, if wo wish 

 to partake really of tea, and not of a brown solution of 

 gum. The tea-leaves have only to be infused with boil- 

 ing-water, and after this the process of boiling must not 

 be continued, or the tea-oil escapes, and the formation 

 of a bitter solution of tannic acid takes place, a decoction 

 wliich could as well bo prepared from oak-apples. The 

 first infusion contains four to six, times more of the pecu- 

 liar constituent of tea than the second. 



Finally, the two principal kinds of chocolate are dis- 

 tinguished similarly to green and black tea. It is true, 

 the cocoa seeds, of which chocolate is prepared, are 

 always roasted. Besides the decomposed fat, an aro- 

 matic empyreumatic substance of dark colour is formed 

 from the starch and gum ; but the proportion of the 

 latter substance is larger in tho more strongly roasted, 

 dark-brown Italian chocolate, than in the Spanish, which, 

 being less roasted, holds more starch and butter of cocoa 

 in an unaltered state. The colour of the Spanish choco- 

 late is brown-red ; it* taste not so bitter and aromatic as 

 the Italian. 



73. Nutritive Qiudities. From its very largo pro- 

 portion of albumen, chocolate is the most nutritious of 

 these three beverages ; but, at the same time, tho most 

 difficult of digestion from its quantity of fat. But as 

 its aromatic substances strengthen the digestion, a cup 

 of chocolate is an excellent restorative, and invigorating 

 ref reshment even for weak persons, provided their diges- 

 tive organs are not too delicate. Cardinal Richelieu was 

 indebted, in his later years, for his health and hilarity 

 to chocolate. 



Tea and coffee do not afford this advantage. Albumen 

 in tea-leaves, and lugumin in coffee-berries, are repre- 

 sented in very scanty proportions, and still more scantily 

 in their infusions : for while in tho former the albumen 

 is coagulated by boiling- water, in tho latter the legumin 

 is prevented from being dissolved by tho lime with which 

 it is combined. 



It is true that coffee and tea have been praised, even 

 by chemists, as nutritious substances, at a time when 

 " nitrogenised" and "nutritious" were considered iden- 

 tical terms. Since then, however, we have learned that, 

 as restoratives for the body, not the elements but the 

 vlimcntary principles are to bo taken into account. The 

 latter appellation cauuot be ascribed to thein, which is 

 excreted again as urea with surprising rapidity. To this 

 swift transformation tea and coil'oo owe their diuretic 

 action, which is considerably assisted by the warm water 

 of tho infusion ; the kidneys attract the urea, with which 

 ;ho thein charges tho blood. 



Tea and cotl'ee, though of themselves not difficult of 

 digestion, tend to disturb the digestion of albuminous 

 substances by precipitating them from their dissolved 

 state. Milk, therefore, if mixed with tea or coffee, is 

 more difficult of digestion than if taken alone ; and coffee 

 ilono, without cream, promotes digestion after dinner, by 

 ncro.ising the secretion of the dissolving juices. No 

 Italian takes cream witli his coffee after dinner. 



The volatile oil of coffee, and tho empyreumatic and 

 iromatic matters of chocolate, accelerate the circulation, 

 which, on tho other hand, is calmed by tho tea-oil. 



Tea and coffee excite the activity of the brain and the 



