298
standard solution of the chloride, to be tested upon a determinate quantity of arsenious aciddissolved in muriatic acid, till the whole arsenious be converted into the arsenic acid. Thevalue of the chloride is greater the less of it is required to produce this effect. It is easyto recognise, by a few drops of solution of indigo, the instant when all the arsenious acidhas disappeared; for then the blue tint is immediately effaced, and cannot be restored bythe addition of a fresh drop of the indigo solution.
In graduating the arsenical chlorometer, M. Gay Lussac takes for his unity the decol-oring power of one volume of chlorine at 32° Fahr., and divides it into 100 parts. Sup-pose that we prepare a solution of chlorine containing its own volume of the gas, and anarsenious solution, such, that under a like volume, the two solutions shall reciprocally de-stroy each other. Let us call the first, the normal solution of chlorine, and the second,the normal arsenious solution. We shall fix at 10 grammes the weight of chloride of limesubjected to trial; and dissolve it in water, so that the total volume of the solution shallbe a litre (1000 grammes measure), including the sediment. If we take a constant vol-ume of this solution, 10 centimetres cube (10 gramme measures), for example, divided in-to 100 equal parts, and pour into it gradually the arsenious solution (measured by likeportions), till the chlorine be destroyed, the bleaching power will be proportional to thenumber of portions of the arsenious solution, which the chloride shall have required.If tne chloride has destroyed 100 portions of the arsenious solution, its title will be 100;if it has destroyed 80 portions, its title will be 80, &c., and so forth.
On pouring the acidulous arsenious solution into the chloride of lime, this will becomevery acid; the chlorine will be emitted abundantly, and the proof will be quite incorrect.If, on the contrary, we pour the solution of the chloride of lime into the arsenious solu-tion, this evil will not occur, .since the chlorine will always find plenty of arsenious acidto act upon, whatever be the dilution of the one or the other; but in this case, the stand-ard of the chlorine is not given directly, as it is in the inverse ratio of the number ofportions which are required to destroy the measures of the arsenious solution. If 50portions of the chloride have been required, the proof will be 100X^ o =200 o ; if 200have been required, the proof will be 100X-|^§~50 o , &c. This evil is not, however,very serious, since we have merely to consult a table, in which we can find the proofcorresponding to each volume of the chloride employed for destroying the constantmeasure of the arsenious solution. The arsenious solution should be slightly tinged withsulphate of indigo, so as to show, by the disappearance of the color, the precise point orinstant of its saturation with chlorine, that is, its conversion into arsenic acid. If thearsenious acid be pure, the normal solution may be made directly by dissolving 4*439grammes of it in muriatic acid (free from sulphurous acid), and diluting the solutiontill it occupies one litre, or 1000 grammes measure. Annales de Chimie et Physigi‘ e ?lx. 225.
CHOCOLATE is an alimentary preparation of very ancient use in Mexico , fr° mwhich country it was introduced into Europe by the Spaniards in the year 1520, and bythem long kept a secret from the rest of the world. Linnaeus was so fond of it, that hegave the specific name, tkeobroma , food of the gods, to the cacao-tree which producedit. The cacao-beans lie in a fruit somewhat like a cucumber, about 5 inches long and3£ thick, which contains from 20 to 30 beans, arranged in 5 regular rows with part*'tions between, and which are surrounded with a rose-colored spongy substance, Jij*that of water-melons. There are fruits, however, so large as to contain from 40 to o*beans. Those grown in the West India islands, Berbice and Demarara , are mucsmaller, and have only from 6 to 15; their development being less perfect thanSouth America . After the maturation of the fruit, when their green color has change
to a dark yellow, they are plucked, opened, their beans cleared of the marrowy su
stance, and spread out to dry in the air. Like almonds, they are covered with a Ijtskin or husk. In the West Indies they are immediately packed up for the man* ^when they are dried; but in the Caraccas they are subjected to a species of slight tmentation, L>y putting them into tubs or chests, covering them with boards or ston ^ £ jand turning them over every morning, to equalize the operation. They emit a g° ^deal of moisture, lose the natural bitterness and acrimony of their taste by thisas welt as some of their weight. Instead of wooden tubs, pits or trenches dugground are sometimes had recourse to for curing the beans; an operation called ear ^ 1(terrer ). They are lastly exposed to the sun, and dried. The latter kind are reckon ,
the best; being larger, rougher, of a darker brown color, and, when roasted, throw
their husk readily, and split into several irregular fragments; they have an agree®mild bitterish taste, without acrimony. The Guiana and West India sorts are SII1 ^,L e yflatter, smoother-skinned, lighter-colored, more sharp and bitter to the taste. # ,
answer best for the extraction of the butter of cacao, but afford a less aromatic ^agreeable chocolate. According to Lampadius, the kernels of the West India _beans contain, in 100 parts, besides water, 53*1 of fat or oil, 16*7 of an albuml ;L orbrown matter, which contains all the aroma of the bean, 10*91 of starch, 7f of gu