Of the alkaloids present in cinchona barks, the four possessing remedial value are, stated in order of merit, quinidine, quinine, cin-chonidine, and cinchonine. Their relative and total proportions are each subject to great variations, in fact no two samples of the bark are alike. Until recently, quinine was the only member of the group admitted into use; but experiment has shown that cinchonidine. and cinchonine are very little inferior to the former as a febrifuge, and it is probable that they will not be thrown away in future. Quinidine is in too small proportion to deserve special notice. Though it is impracticable to state the percentage of alkaloids, individually or collectively, in each species of bark, the latter are nevertheless distinguished by well-marked characteristics, a knowledge of which is essential for their most economical and suitable employment. Pale or crown bark is rich in crystallizable quinine, and is highly valued by the manufacturers of quinine sulphate in this country. Yellow bark is even more highly esteemed for this purpose. Red bark, on the other hand, while as rich as either of the others in total alkaloids, contains only little quinine, and that difficult of extraction.
Moreover, this species is hardier, grows better, and yields about 1/3 more bark than officinalis, so that as a source of total alkaloids it is more deserving of attention than the other two, though inferior to them if they could be got to grow as luxuriantly. The red bark, too, is the most valuable for the preparation of tonic decoctions, tinctures, etc, largely used in Europe; and in consequence of this fact, its price in Western markets is but little, if at all, inferior to that of the kinds richer in quinine. The barks best adapted for quinine-making fetch the best prices in European markets, and will probably continue to do so. Red bark will doubtless recede in price when production increases, as the demand for that kind is limited in Europe; it is, however, the only kind likely to be used in the East for the local manufacture of a febrifuge, as efficient as, while much cheaper than, sulphate of quinine. Two conditions bearing upon this part of the subject are: - (1) That high temperature increases the cinchonidine at the expense of the quinine, so that barks grown at a low elevation (or even at a high elevation, if exposed to sunlight), will be richer in the former and poorer in the latter, while a low mean temperature, within certain limits,, favours the production of quinine; (2) That deprivation of light, without impeding the access of air and sun-heat, materially increases the proportion of total alkaloids.
The manufacture of a cheap febrifuge has engaged the serious attention of the Indian government, resulting in two such products - Broughton's " amorphous quinine," and the febrifuge called "quinetum " by Dr. de Vrij.
The former is prepared in the following way: - Strips of the bark are placed in a copper pan with sulphuric acid (1 1/2 per cent, for trunk-bark, 1 per cent, or less for prunings, &c), and a quantity of water from the fourth extraction" (v. post); the whole is boiled for 1 hour, then subjected to a strong screw press, the liquid being caught in a wooden vat. The bark is reboiled with liquor from a third extraction, with an additional 1/2 per cent, of acid, for 1 hour, and is again squeezed. A third boiling is given in liquor from a fourth extraction, and, after squeezing, the bark is finally boiled with fresh water, sun-dried, and used as fuel. The resulting concentrated decoction is evaporated to 1/6, and cooled; it is then decomposed by addition of milk of lime in slight excess, which precipitates the alkaloids, with formation of insoluble lime salts; after standing for a day, the precipitate is filtered off, squeezed, dried, and powdered. The powder is then placed in the apparatus shown in Fig. 5.; A B C D is a sheet-iron cone, traversed by an upright tube E, terminating above in 4 open arms, and supported below on a flat iron disc CD. A copper vessel FG fits closely to the lower end of the cone.
The latter is . suspended, and connected, through the tube H, with a simple worm tub. The cone is packed with the precipitate up to E, the lid is put on, and alcohol is added slowly from above, till FG is about 1/3 full of the saturated spirit, which is then carefully neutralized by dilute sulphuric acid. The cone is then connected with the condenser through H, and a fire is lighted below. The spirit boiling in F G rises in vapour through E, passes out at the openings, and condenses so as to form a liquid stratum above the precipitate. This is observed by the gauge B I; uncondensed vapour passes through H, and is caught. A small quantity of spirit, by constant circulation, extracts all the alkaloids without waste. The alkaloid in F G is neutralized with dilute acid every two days. When the precipitate no longer contains any alkaloid, F G is removed, and the alcohol is distilled off; the alkaloid is washed with water, while the alcohol is recovered with a maximum loss of 6 per cent. The alkaloid is treated suddenly with about 10 times its bulk of cold water, which separates the black resin present; the addition of a little dilute acidulated solution of sodic sulphide will remove any copper accidentally present.
The alkaloid solution being still coloured, a small quantity is precipitated by dilute caustic soda, the colouring matters falling at the same time. The whole is then filtered through cloth; and the alkaloid is precipitated by caustic soda, filtered, pressed, dried, and powdered. Potash may replace soda, if more easily or cheaply procurable. This process was employed to produce 600 lb. of alkaloid in the Nil-giris; but the product was found to cost more than ordinary commercial quinine, assuming the value of dry trunk-bark at 2s. a lb., and branch-bark at 6d. The yield of alkaloid is, however, naturally much greater.