We know that in boiling starch with dilute sulphuric acid, it is promptly converted into dextrine and glucose. At whatever period of the operation we may examine the liquid, we find in it free sulphuric acid, and always in the same quantity; but the reaction, which consists in a simple fixation of water, goes on the more rapidly the more sulphuric acid is employed.

We may effect the same transformation by using nitric acid, and thus obtain an intermediate product which possesses some interest. Take, for example, forty parts of dry starch, and moisten it with one and a half parts of water, and then add two per cent. (of the starch,) of nitric acid-leave this mixture to dry, at first in the open air, and then in a water bath. The dry mass is to be dissolved completely in water, and in using but five parts of water to one of starch, the solution gelatinizes on cooling. In this state it much resembles dissolved starch (empois) that many of the masses supply, and which is commonly prepared from lichens, or seaweed. If this solution be boiled a long time, and especially if a little acid be added, it loses the property of gelatinizing. The formation of dextrine and glucose is due to the fixation of water determined by the action of the acids.

The conversion of starch into dextrine may also be effected by the aid of a temperature of 150°. Thus the acids and heat operate precisely like platina and heat in the combination of hydrogen and oxygen. Diastase, at the temperature of 75°, acts, with respect to starch, like acids. As this substance has not hitherto been obtained in a state of purity, we cannot prove that it has not undergone some alteration during the transformation of starch; and yet, since the reaction is effected by so very small a quantity of diastase, even when impure, we may reasonably admit that it acts only and truly by contact.

A few hundredths of sulphuric acid added to a solution of cane sugar, is sufficient, even in the cold, to change it to glucose, and to enable us to prove its existence in the fluid by sulphate of copper and potash. Other acids transform it also in the cold. Acetic acid does the same, but only when hot.

It is for this reason that lime is added to the saccharine juice of plants when cane sugar is to be extracted. I have examined the juice of beets, and have always found it perfectly neuter, so that the transformation we have spoken of is impossible in the beet itself; but every wound may become the cause of the production of acids, and then the sugar is subjected to alterations.

I have obtained the sugar derived from the action of sulphuric acid on cane sugar in the state of crystals. The sugar obtained by adding beer yeast to a solution of cane sugar, appears to differ from grape sugar. I have not been able to obtain it crystalized, and it rotates polarized light much less than an equal quantity of grape sugar. Its formation is very remarkable; it is owing to a substance mingled with the globules of ferment; it is the aqueous solution of this material which determines the change of cane sugar into this new kind of sugar. On this account fermentation takes place much more slowly in a solution of cane sugar, when washed yeast is employed instead of common yeast. In the former case, give common yeast the time

necessary for a part of it to become transformed into this soluble body. Common yeast excites fermentation as quick in a solution of cane sugar, as in one of glucose.

This kind of sugar differs in other respects from that obtained by melting cane sugar.

In melting cane sugar at a temperature of 160 degrees, it becomes completely deliquescent, dissolves in absolute alcohol, ferments when put in contact with a ferment, and exerts on polarized light much less influence than that of grape sugar.

Cane sugar, after being melted, no longer crystalizes; but if melted with water, care being taken not to raise the temperature above 154°, it produces, on cooling, a vitreous mass, composed chiefly of cane sugar and water mechanically enclosed. The latter dissolves the particles of sugar one after another, and deposits them in crystals, for an amorphous body is more soluble than a crystalized body. The whole mass passes to the crystaline state. It is easy, in breaking a stick of such sugar, to perceive the presence of water, especially near the centre, and among the crystals. It is possible that this sugar may be identical with that procured by keeping a solution of cane sugar a long time at the temperature of 110°, and which, according to M. Fensky, exerts no action on polarized light. Perhaps it is identical also with that which M. Peligot and M. Mulder, procured by boiling cane sugar a long time with dilute acids, and which, they say, does not crystalize.

Chemists are agreed relative to the changes which glucose and other kinds of sugar undergo during fermentation. It is generally admitted that carbonic acid is formed with a third part of the carbon of the sugar, while the remaining two-thirds unite with the hydrogen and oxygen to form alcohol. Thus for one measure of carbonic acid, one measure of alcohol is produced; but, according to the kind of sugar, there is an elimination, or a fixation, of water; the first case presents itself in glucose, the second with the variety of sugar soluble in alcohol. The body which determines this action, the only means by which it can be produced, is an organized body.

We may, without entering into a detail of the opinions to which this phenomenon has given rise, discuss the facts which alone possess any interest in this question. Ferment is composed of oval and round globules; these globules are large enough to be retained by filtering paper. If we put a small quantity of ferment into a tube closed at one end with blotting paper, and introduce it into a solution of sugar, the latter passes through the pores of the paper, and undergoes the alcoholic fermentation, but only in the tube which contains the ferment. The fermentation goes on in the solution in which the tube has been placed only after a longer, or shorter, period, and always under the influence of globules of ferment, which eventually pass through the pores of the paper, which softens by its prolonged contact with the liquid. This experiment plainly proves that fermentation goes on only at the surface of the globules of ferment.

I have made other experiments which prove what has just been advanced. M. Schwann has made others, but they are not so deci

sive as those just stated. I have never seen fermentation without globules of ferment, and the phenomenon always appears at the surface.

It requires but one per cent. of globules of ferment to effect the complete transformation of sugar into alcohol and carbonic acid, and when we use globules perfectly organized, they undergo almost no change during the fermentation. When destroyed they are no longer effective. In placing them in contact with bodies which have the property of arresting fermentation, we perceive them to contract when examined by the microscope, at the moment of touching these bodies.

Globules of ferment therefore when mingled with sugar, or sugar and water, which contain the elements of carbonic acid and alcohol, act precisely like spongy platina, with respect to oxygenated water.Naturalists, occupied with the study of the most simply organized beings, declare that globules of ferment ought to be ranked among them; and, in reality, considering their generation and development, we can come to no other conclusion. Thus, generation always takes place in the fermentable juices of plants, and before fermentation commences in them.

It is only at the end of three days that we remark in these liquids microscopic points, isolated, or united into chaplets;-these points expand, and we may plainly perceive that their increase occurs from within outwards; and eventually we observe in their interior a granulated mass surrounded with a transparent envelope. They are often elongated, and then they exhibit two or three granular points.

By using perfect globules of ferment for exciting fermentation in sugar, I have not perceived them to develope; but by leaving the ferment for some time they are seen to ramify in the manner of confervæ. The organized beings that are formed in whey ramify in whorls. The sediment which occurs in whey in the course of a few days, is, like ferments, organized, but mingled very often with unorganized substances. Agreeably to several naturalists-MM. Schultz, Schwann, and others—these beings are not reproduced when access of air is prevented, and never when matter susceptible of being converted into ferment, are fed with air previously exposed to a red heat. This is one proof against equivocal generation, while the supposition that the origin of an organized being in a liquid springs from a point that escapes observation, leads to a conclusion favorable to such genera

tion.

It would be important to know what these beings would become, if, instead of being developed in a liquid, their expansion took place in the open air. Would it result in a mucor, as M. Kutzing supposes? A mucor added to a fermentable liquid excites no fermentation, and moist ferment, long exposed to air, is not transformed into

mucor.

The presence of these organized beings in the intestinal tubes of herbivorous animals possess a special interest; we may assure ourselves, by the method of M. Tromener, that there is grape sugar in an animal which has eaten vegetable food. It is found in the stomach,

and intestinal tube, as far as the rectum only. We find great numbers of organized beings in these parts of the organism, but they disappear entirely in the rectum and in the fecal matter. M. Remac first drew my attention to this, and since then M. Purkinjes, M. Bohn, and my brother, have had occasion frequently to observe them. It is very probable that in addition to digestion, a true alcoholic fermentation takes place in the intestinal tube occasioning ventuosities. The blood which surrounds the intestinal tube, dissolves carbonic acid, which may be disengaged by the lungs without recurring to other modes. These organized beings, commonly of an elliptical form, have two transparent points, and sometimes enclose a granular mass like those of ferments.

MM. Boutron and Fremy have recently proved that lactine is transformed into lactic acid under the influence of caseum, and that this combines with the acid formed. Further, in separating caseum from its combination with lactic acid, by means of carbonate of soda, a fresh quantity of it is produced. The composition of lactic acid is such that it is represented by sugar of milk, minus a certain quantity of water. I have repeated these experiments with the same results; but, as in this reaction, a compound is formed of caseum and lactic acid, we must suppose that the affinity of lactic acid for caseum intervenes in the phenomenon. The coagulation of milk, however, in the preparation of cheese, seems to be owing to other causes, since rennet is commonly employed to produce it.

We generally suppose that it is the internal part of the stomach of the calf which causes the coagulation of milk. It is not so, however; the rennet that I obtained was prepared from mucus and the muscular membranes which are taken from the stomach, rejecting the peritoneum: but I could easily coagulate milk by making use of other parts of the peritoneum,-the part, for example, which covers the cæcum.

When we take the precaution to raise the temperature of milk a little, coagulation takes place in a few hours, either by suspending the membrane in it, or pouring into the milk a warm infusion of it. The membrane and its infusion have no acid reaction, and the milk remains neuter during its coagulation.

The chemical combinations which are established by means of substances which act only by contact, are very analogous to those which are produced, when, for example, one body combines with a second, and the resulting compound acts upon a third.

Sulphurous acid has more affinity for oxygen than the binoxide of azote; and yet sulphurous acid does not combine with oxygen when we allow the mixture of these gases to remain long in contact, whilst the binoxide of azote directly seizes gaseous oxygen to form hyponitric acid. The latter yields its oxygen to sulphurous acid to become again binoxide of azote. The oxygen then in hyponitric acid is in a state which enables it to combine with sulphurous acid. Putting a mixture of oxygen and sulphurous acid in contact with spongy platina, the two gases combine; the action of the platina is, therefore, in this case, the same as in hydrogen and oxygen.

All these processes, and especially the production of the ethers, and of the ether itself, lead to the conclusion that chemical decompositions and combinations may be prevented by the respective position of the atoms; but that the force of attraction which certain bodies exert on the atoms of those into whose presence they are placed, may change the position of them in such a way as to determine chemical reactions. The manner in which gases act with charcoal, and especially with platina black, proves that this attraction is very strong even with respect to bodies of different natures.

Berzelius gives to this force the name of catalytic force, with as much reason as we say force of affinity, &c., and understand by this denomination a force which is appropriated to many substances which do not enter chemically into the reactions which they excite, and whose activity consists in destroying chemical combinations. In order to affix a term to the phenomena, I have named these substances contact substances, (contact substanzen,) and the chemical process, a decomposition, or a combination by contact.

Notice of the Manufacture of Gluss in Bohemia. By M. L. P. DEBETTE. [Annales des Mines, 4th series, volume iv, page 553; December, 1843.]

TRANSLATED FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.

(Continued from Page 192.)

CHAPTER IX.-Of Opalescent Glass.

The milky-white glass imitating alabaster, or opal, is prepared like the fine colorless glass, only with the addition of a greater, or less, quantity of calcined bone powder, according as a more or less opaline glass is desired. A great quantity of opaline glass colored green, is also manufactured in Bohemia; formerly it was prepared by adding to colorless glass a certain quantity of calcined bone powder, yellow oxide of uranium, and oxide of iron, (finery cinder.)

This color is altered after long exposure to solar light. For some years past it has been replaced at Winterberg and at Silberberg, by a more beautiful color, due to calcined bone powder, yellow oxide of uranium, and oxide of nickel. The oxide of tin is employed solely in the manufacture of enamels, because it is far more dear than the calcined bone powder, (phosphate of lime-bone earth,) and because it requires a larger quantity to produce the same effect.

CHAPTER X.-Of Hyalite.

The name hyalite is given to a completely opaque glass, generally black, which is distinguished by a hardness and lustre truly remarkable, and forming a beautiful contrast with gold. It may without any inconvenience, be employed for the manufacture of vessels intended to hold boiling liquids, such as tea-pots, coffee-cups, &c., without any danger of its breaking. It was first made in 1820, at