It has now become commercially practicable to prepare alcohol synthetically, as well as by the fermentation methods. The raw material employed is the hydrocarbon gas acetylene, C2H1 - or rather calcium carbide, which readily yields acetylene on treatment with water.

Acetylene can be converted into ethylene, C2H4, or into aldehyde C2H4O, either of which substances can furnish alcohol.

Calcium carbide, CaC2, is obtained by heating a mixture of coke and lime in the electric furnace.

Another carbide is said to have been produced which yields ethylene directly, instead of acetylene, when treated with water. The particulars have not been disclosed.

Enzymes.

As already indicated (p. 17), enzymes play a very important part, both in the production of sugar from starch and in the con-version of sugar into alcohol. They are nitrogenous compounds, either albuminoids or very closely related to albuminoids in composition, which occur in all living organisms, whether animal or vegetable. Their function in the organism appears generally to be to attack insoluble materials intended for the sustenance of the animal or plant, converting them into more soluble and more diffusible substances, and thus making them more available for nutrition. Ptyalin, for example, the enzyme contained in saliva, and also amylopsin, present in the juice of the pancreas, both have the power of converting insoluble starch into soluble sugar. They thus resemble diastase in their action. The pepsin of the gastric juice, and the trypsin of the pancreas, each converts insoluble proteids into simpler proteoses and peptones, rendering them more fit for absorption; whilst lipase, which occurs in the pancreas and also in various seeds, splits up fats into glycerol and fatty acids. The zymase of yeast converts sugar into alcohol and carbon dioxide; the maltase of malt transforms the 12-carbon sugar maltose into the 6-carbon sugar dextrose.

Thus the enzymes can be classified into groups according to the kind of action which they exert. Chief among these groups for

1 Motor Union Fuels Committee, Report, p. 50., our present purpose are (i) the diastatic enzymes, which hydrolyse starch; (ii) the inverting enzymes, which transform cane-sugar into invert-sugar, or maltose into dextrose; (iii) the alcohol-producing enzymes, e.g., zymase and its co-enzyme; and (iv) the proteolytic enzymes, which convert proteins into simpler bodies such as peptones and amino-acids.

Enzymes are soluble in water, and are coagulated by heat. From their aqueous solutions excess of alcohol separates them as amorphous, white precipitates, as also does ammonium sulphate. The precipitated enzymes are dissolved by glycerol, and these solutions can be preserved for a considerable time: the solutions in water soon decompose. When completely dry, the enzymes may be exposed to temperatures as high as 100 to 125° without destruction of all their characteristic properties; but in aqueous solution a temperature of 80 to 90° usually destroys their activities. They act at ordinary or slightly elevated temperatures; below 0° their activity is suspended, and it is lessened at about 60°, though they are not all equally sensitive to the effects of heat. There is a limited range of optimum temperature for every enzyme; thus diastase acts best at about 50-55°, and invertase at about 55°.

One notable fact about enzymes is that a very small quantity will suffice to transform a relatively enormous amount of the substance acted upon. Thus one part of invertase (sucrase), according to O'Sullivan and Tompson, can invert 200,000 parts of cane-sugar. In this respect, the enzymes resemble catalysts, and they are also similar in the fact that they are very sensitive to the presence of certain chemical substances, such as hydrocyanic acid, formaldehyde, and mercury salts, which render them inactive, much as catalysts are "poisoned" by minute quantities of certain bodies.

Another remarkable fact- is that a given enzyme can only act upon a certain class of substances: it has its own specific action. Diastase hydrolyses starch, but not proteids; pepsin attacks proteids, but not starch. Neither of these will split up fats; whilst lipase, which does this, cannot break up either carbohydrates or proteids. Further, there are several examples of sugars, which exist in two optically isomeric forms, and of which one isomer is susceptible to the attack of an enzyme, while the other remains unaffected. Thus d-glucose is fermented by certain yeasts, but l-glucose is not. These facts suggest that there is a close resemblance in structure between an enzyme and the substance which it attacks. They have led to the hypothesis that the molecular configuration of the enzyme and that of the sugar it ferments are complementary, so that "the one may be said to fit the other as a key fits a lock ' (E. Fischer), or " as male and female screw " (Pasteur). Nothing, however, is actually known of the molecular structure of the enzymes.

According to Adrian Brown,1 the enzyme invertase in its action on cane-sugar combines with the sugar to form a molecular compound, which does not decompose instantaneously, but exists for a perceptible interval of time before final disruption. O'Sullivan and Tompson had previously shown that the activity of invertase in the presence of cane-sugar survives a temperature which completely destroys it if cane-sugar is not present, and they regarded this as indicating the existence of a combination of the enzyme and sugar molecules.2 Wurtz3 had also shown that the enzyme papain appears to form an insoluble compound with fibrin previous to the hydrolysis of the latter.

It may be noted that in modern enzyme terminology the ending "ase" is used to denote an enzyme, the first part of the name indicating the substance attached by the enzyme. Thus the enzyme maltose attacks the sugar maltose; lactase attacks lactose; and so on. Hence the modern term for diastase is amylase (amylum, starch), and for invertase, sucrase, since this enzyme attacks sucrose. But the older terms are frequently used, especially the long-established ones, like diastase.