August i, 1884,] 



THE TROPICAL AGRICULTURIST. 



127 



over the body, while the abdomen is terminated by two 

 long and fine filaments. The females, on the contrary, are 

 wingless, almost limbless, and remain fixed to the spot on 

 which they are placed or to which they attach themselves. 

 Of this numerous family of insects, many of which are 

 very troublesome and destructive, there are at least three 

 distinct species which are of considerable commercial value, 

 and which are, in consequence, more or less carefully pro- 

 tected or cultivated, namely, the Coccus lacca, the Coccus 

 ilicis, and the Coccus cacti. The Coccus lacca is a native 

 of Siam, Assam, Lurmah, Bengal, and Malabar, and yields 

 the various products known under the general name of 

 "Lacs." The insects attach themselves to the branches of 

 a tree, and propagate with such marvellous rapidity that they 

 quickly cover the whole surface. During their short lifetime 

 they secrete a resinous colouring matter, which is perm- 

 anent, and, being constantly increased as generation after 

 generation is propagated, soon forms solid masses of con- 

 siderable thickness. These masses the natives collect and 

 treat in various ways, and thus produce all the varieties 

 of lacs known in commerce. 



The Coccus Uicis, known as "Kermes," is abundant in 

 various parts of the South of Europe, and also in India 

 and Persia. The female insect burrows under the epidermis 

 of the leaves or young shoots of the Kermes oak (Quercus 

 coccifera), where it grows and swells, covering the leaves 

 and branches with a series of excrescences, in which the 

 eggs are deposited and where the iusect finally dies. The 

 kermes is gathered before the eggs are hatched, and pro- 

 duces a colouring principle which has been known and used 

 from ages so remote that it is supposed to have been the sub- 

 stance used in dyeing the curtains of the Jewish tabernacle. 



The third species, with which we have more immediately 

 to do at present, namely, the Coccus cacti, has only bei □ 

 known in Europe from about the beginning of the sixteenth 

 century. It was originally discovered in Mexico, and only 

 of recent years has it been introduced and propagated in 

 the Canary Islands, the island of Teueriffe and Algeria. 

 It lives on the plants of the cactus family, and particularly 

 on one, commonly designated the " Cochineal Plant," but 

 known to the natives as the " Nopal" (Opuntia cochinilli- 

 fera, or Cactus opuntia). The nopal plant is indigenous to 

 Mexico, where it grows wild, but it is also largely cultiv- 

 ated, and the insects obtained from the two sources, namely, 

 from the wild and cultivated plants, differ in their com- 

 mercial value, that from the former being of inferior 

 quality. This is called Grana silvestres, and is smaller than 

 the Grana fina (cultivated), also called Mesteque, from the 

 name of a province. At the proper season the natives take 

 the young female insects, which have been carefully pre- 

 served on the stems of the cactus from a previous crop 

 (the succulency of the plant permitting of their being kept 

 for a considerable period), and placing them on the young 

 plants they quickly grow and multiply. Three months is 

 about the time allowed to elapse between the sowing, if it 

 may lie called so, of the insect and the gathering in of 

 the new crop. At the proper season the insects are swept 

 off the leaves of the nopal plant into convenient recept- 

 acles, when they are either killed by a momentary immer- 

 sion in boiling water or by heating them in ovens, and less 

 frequently stdl by exposure to the sun. According to the 

 different modes of killing the insect is ascribed the ap- 

 pearance of the cochineal as brought to the market, those 

 thrown into hot water and afterwards dried forming the 

 dark (negro), while those placed in bags and heated in ovens 

 constitute the silver (bianco). 



CHEMICAL HISTORY, &C. 



The colouring principle of cochineal was first separated 

 in an impure state by Pelletier and C'aventou. by treating 

 the cochineal first with ether to extract the fatty matter, 

 and afterwards digesting the residue in heated alcohol. 

 Some idea of the colouring-power of cochineal may be 

 gathered from the fact that thirty infusions with alcohol 

 were required before it ceased to yield colour, and even 

 then it was not exhausted, as was proved on adding other 

 media to the digester. The percolates on cooling deposited 

 a bright red granular mass, which on spontaneous evapor- 

 ation assumed somewhat of a crystalline structure. The 

 colouring principle thus obtained was considered by Pelletier 

 to be an azotised compound, but Dr. Warren de la Rue; 

 who subsequently investigated this colouring principle, 

 found that it contained no nitrogen, and that it had the 



formula O14H14O8. As this compound had distinct acid 

 properties he gave it the name of "Oarminio Acid," and 

 this name has become very much synonymous with carmine, 

 carmine of commerce when pure being simply carmiuie 

 acid plus a small percentage of the precipitating agent, 

 such as alumina, oxide of tin, or albumen. Carmine is 

 prepared in a variety of ways, but the variation, il will 

 be found, consists as much in the different preeipitants 

 used as in auy disiiuct variation of the product itself. 



An aqueous infusion, for example, is prepared, and bi- 

 chloride of tin added, and the whole put into shallow 

 vessels, when carmine slowly deposits on the sides of the 

 vei Or cochineal is added to boiling water and allowed 



to iufuse for a few minutes, whin powdered alum is added 

 and the mixture again brought to the boiling-point, allowed 

 to cool, filtered, and set aside to deposit. Or this process 

 may be varied by adding, previous to the alum, a certain 

 proportion of cream of tartar. Or the cochineal may be 

 boiled with carbonate of potash, to which the alum is 

 afterwards added. Carmine is insoluble in ether, is soluble 

 without decomposition in sulphuric acid, hydrochloric acid, 

 and ammonia, while chlorine, on the other hand, has a' 

 powerful decomposinginfluence upon it. An aqueous solution 

 gives a beautiful crimson red with caustic alkalies, while 

 oxymuriate of tin and cream of tartar or oxalate of potash 

 give respectively a red and an orange red precipitate. An 

 aqueous infusion of the coftineal, it maybe well torenu 3mbi r- 

 changes to a reddish yellow on the addition of tincture 

 of galls or stronger acids, and to a deep violet with lime- 

 water, while it is precipitated deep reel by alum, bright 

 red by ammonia, violet blue by neutral acetate of lead, and 

 dark brown, changing to olive green, by ferric chloride. 



ADULTERATIONS, &f. 



From it expensive nature cochineal has always been sub- 

 ject to adulterations, and much ingenuity has often been 

 expended in perpetrating frauds of this nature. -One of 

 the most common is to deprive the cochineal of part of 

 its colour by immersing in water and afterwards drying 

 it, when it is sold as the dark (nigra), or it is "doctored" 

 with various substances and boldly sold as the silver (bianco^ 

 cochineal. To detect frauds of this kind, as well as to test 

 the value of inferior cochineal generally, recourse is had 

 to one of several methods of estimating its tinctorial power. 

 The simplest plan probably is to exhaust a weighed portion 

 of the sample with a given quantity of water, and com- 

 pare with a standard sample by the help of a colorimeter. 

 Another plan is to compare the colour imparted to wooi 

 with that yielded by a standard cochineal, this plan being 

 the one generally adopted by dyers. Probably the better 

 plan is to decolourise the infusion of a given quantity by 

 a standardised solution of chlorine or chlorinated lime or 

 to precipitate the carmine with hydrate of alumina. 



Dr. Crace-Calvert gives very good forms for estimating 

 its dyeing-power on wool or flannel. The bath for scarlet 

 tints is composed as follows: — Cochineal, 1 part; tin com- 

 position, 2 parts; cream of tartar, 2 parts ; water, 1,250 parts. 

 For the crimson bath: — Cochineal, 1 part; alum, 1-5 part; 

 cream of tartar, -75; water, 1,250 parts. The pieces dyed 

 in these solutions are afterwards washed and dried, and 

 by a comparison of the relative shades, the value of (he 

 cochineal is determined. A considerable number of years 

 ago a very systematic process of adulterating cochineal 

 was discovered, whereby nearly 12 per cent of worthless 

 matter was added to it. The fraud was apparently per- 

 petrated something after' the following manner: The 



cochineal was first damped with thin mueUage, then shaken 

 with sulphate of barium, and finally with ivory black, and 

 dried. This gave it the appearance of dark cochineal^ and 

 the fraud seems to have been carried on for years. An 

 exposure such as this is almost certain for a time to put 

 a stop to the fraud from the very publicity which is given 

 to it. There is, however, every reason to believe that 

 such adulterations are still extensively carried on, and with 

 an ingenuity so great that even good judges are often im- 

 posed upon. In addition to the adulterant alreadymentiom d 

 carbonate, chloride, and sulphate of lead, oxide of man^ 

 oxide of iron, and other heavy substances are also frequently 

 employed. To detect all such it should be kept in mind 

 that the pure cochineal should not yield more than 5 per 

 cent of ash, while after combustion' the ash may l< 



i and afterwards estimated in the ordinary manner 

 for non-organic compounds. 



