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Cactus nopal or Opunta coccinilifera. This plant is in-digenous to Mexico, where it grows in the wild state ; and from it large quantities of cochineal are col-lected. It is also extensively cultivated by the native Indians, who often bave plantations containing 60,090 plants. The cochineal obtained from the two sources is of different quality ; that from the cultivated plant is much superior, and is called mestique ; that collected from the wild plant is called sylvestra.

I will now explain, in a few words, how cochineal is propagated and prepared for market. In the month of May, in the flat lands, and in November in the moun-tainous districts, the Indians take the stems of the cactus, which they have preserved from a previous crop, and remove from them the young female insects, which are placed on the growing plants, where they grow and multiply with great rapidity. After a period of about three inonths, the insects are collected into small tin dishes, so formed as to enclose the bottom part of the plant, and by means of a small brush they are swept from each stem successively into it. They are then destroyed, either by being thrown into hot water and afterwards dried in the sun, or in stoves, which gives the black cochineal, called zacatilla or they are placed in a bag and stoved at once, which leaves upon them that peculiar lustrous appearance which characterises the silver white cochineal, called blanco. Although one pound of cochineal contains 70,000 insects, there are millions of pounds imported into Europe every year.

If one of the dried insects be placed in warm water it swells, and takes a hemispheric form, when its structure can be seen. If it is pressed between the Angers, thou-sands of little red grains are exuded, which, if placed under the microscope, are seen to be minute cochineal insects.

The colouring principle was first isolated in an impure state by Pelletier, who considered it to be an azotised compound. MM. Arppe and Warren de la Rue, however, found that it contained no nitrogen, and that it had the formula C14 Hi4 O8. As it had distinctly acid pro-perties, they gave it the name of carminic acid. M. Schützenberger proved that carminé is composed of carminic acid and an organic azotised base, called tyrosine.

MM. Arppe and Warren de la Rue obtain crystallised carminic acid by the following process. The cochineal is treated with ether, to remove fatty matters, then boiled in water. An acid acetate of lead is added to the solution thus obtained, which précipitâtes an insoluble carmi-nate. This, after being washed carefully, is decomposed with sulphuric acid, the carminic acid being liberated. The aqueous solution is evaporated to dryness, and the mass treated with alcohol, which, on évaporation and cooling, yields it as a crystalline mass.

As shown by the above process, carminic acid is insoluble in ether, but soluble in water and alcohol. It isdis-solved without décomposition by concentrated sulphuric and hydrochloric acids. Carminic acid yields on fabrics, especially on wool, one of the fastest colours known, light and air having no action on it. Chlorine, however, easily destroys it. An aqueous solution of the acid gives the following characteristic reactions. With caustic alkalies, it givesabeautiful crimson-red colour ; with oxy-muriate of tin, it gives a red precipitate ; and with cream of tartar or oxalato of potash, an orange-red precipitate. Alumina removes the whole of the colouring-matter from an aqueous solution. As cochineal is an expensive dye-stuff, it is subject to much fraud and adultération. One of the most common frauds is practised at Nismes and other places where perfumery is largely prepared. The cochineal in those localities is put into water for a short time, by which a part of its colour is extracted ; it is then dried, and either sold as black cochineal, or placed in a sack and shaken with talc or sulphate of lead, and sold as white cochineal. This fraud is easily detected by grind-ing the cochineal and mixing it with water, when the

talc or sulphate of lead falls to the bottom. G-ood cochineal does not leave above five or six per cent, of ash.

It is often advisable before buying cochineal to détermine its tinctorial power. This may be ascertained by two or three methods. In the first, equal weights of the cochineal to be assayed, and of one of known value, are treated with alcohol or a solution of alum. The solutions thus obtained are poured into tubes, and placed in a coloro-meter. This is an oblong box, which has two apertures at each end and two on the top, in a direct line with the end apertures. The tubes are placed through the open-ings on the top, and, on looking through the end apertures, any différence in intensity of colour between the two liquids can be observed. If a différence is detected, alcohol or water is added to the stronger liquor until there is perfect uniformity of tint. According to the amount of dilution required is the relative value of the cochineals.

A good process was published by the late Dr. Penny, of Glasgow. It consista in exhausting a gramme of cochineal with 50 grammes of potash solution, and this extract is further diluted with 100 grammes of water. The solution thus obtained is mixed with a graduated solution of ferricyanide of potassium (one gramme of sait to 200 grammes of water) till its colour changes to a dark brown. A solution of bleaching powder of known strength can also be used for the same purpose. The best method consista in dyeing equal surfaces of flannel in a bath composed as follows :—

For Scarlet Tints.

grammes.

Water ............................ 1,250

Cream of tartar ...................... 2

Tin composition ...................... 2

Cochineal ............................ 1

For Crimson Tints.

grammes.

Water ............................ 1,250

Cream of tartar ..................... 0'75

Alum.................................. 1'50

Cochineal ......................... 1

The pièces are then washed and dried, and by a com-parison of the relative intensity of shade the value of the cochineal is determined.

The chief employment of cochineal is for dyeing wool, but it is also employed in calico printing to produce pinks and reds in steam styles.

It will no doubt be interesting to you to know how to détermine whether a pink bas been produced from a dyewood, a cochineal, or from madder. All these colours are destroyed by chlorine or bleaching-powder. A boiling soap solution destroys the wood pinks, communicates a crimson hue to the cochineal dye, and brightens the madder colour. Dipped in a rather dilute solution of hydrochloric or sulphuric acid, fabrics dyed with cochi-nealare notaffected, while those dyed with madder or woods assume a yellow tint, which becomes purple when placed in milk of lime. These cloths, however, if subsequently soaped, will yield their colour if dyed with wood, but not if dyed with madder.

Ammoniacal Cochineal.—When one partof ground cochineal is left in contact with three parts of ammonia for several weeks, a Chemical action ensues, by which the ammonia loses one équivalent of hydrogen, which unités with an équivalent of oxygen of the carminic acid, giving rise to water and an amide compound, carmina-mide. Adopting M. Schützenberger’s formula for carminic acid, the change may be thus represented:—

Carminic Acid. Ammonia. Water. Carminamide

Co Hs Os + NHa = h2o + c9h9no4.

This compound is also used for dyeing, but before em-ploying it for this purpose, it is necessary to add 4 per cent, ot alumina, in the state of jelly, to the mixture des-cribed above. The mass is then slowly evaporated to

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