Take two ounces of flour, boil it in a quart of water, till it comes to the consistence of a thin jelly, pour it into a machine for impregnating water with fixed air; then put into the lower vessel some coarse powdered marble, and pour on it some sulphuric acid diluted with water. The apparatus is now to be adjusted, and the upper vessel put in its place, and nearly stopped. The fixed air now passes through the valve, and ascends into the middle and upper part of the machine, where the gas is absorbed by the flour jelly in considerable quantity; and in the course of a few hours the matter will be found so strongly impregnated, as to be in a state of fermentation. This artificial yeast may now be put into a bottle for use. The great advantage of this yeast is, that it may be made in situations where it is impossible to procure brewers' yeast. The foregoing operation need not be performed but once by the same individual, as the process may be carried on by mixing this artificial yeast, which was invented by the late Mr. Henry, with the preceding preparation recommended by Dr. Lettsom, which it will cause to ferment the same as brewers' yeast.

Another artificial yeast is made as follows: - Take half a pound of fine flour, the same quantity of coarse brown sugar, and a quarter of a peck of bruised malt; boil these over the fire for a quarter of an hour, in half a gallon of water, then strain the liquor through a sieve into an upright jug, and when cooled to 80 degrees of heat, add one pint of the artificial Seltzer water, or, if procurable, Seltzer water itself, or water impregnated with fixed air - the mixture will soon begin to ferment: it should then be set before the fire, and when ebullition ceases, the yeast will sink to the bottom. Pour off" the clear liquor, and the yeast will be fit for use.

Patent Yeast, which is extensively used by the London bakers, and which is, perhaps, preferable to all other yeasts, is made as follows: - Take half a pound of hops and two pailfuls of water, mix and boil in the oven till the liquid is reduced to one pailful; strain the decoction into the seasoning tub, and when it is sufficiently cool put in half a peck of malt. In the mean time, put the hops, strained off, again into two pailfuls of water, and boil as before till they are reduced to one; strain the liquid while hot into the seasoning tub. The heat will not injuriously affect malt, previously mixed with tepid water. Boil the hops again as before, and strain off as before into the seasoning tub. When the liquor has cooled down to about blood-heat, strain off the malt, and add to the liquor two quarts of patent yeast set apart from the previous making. It ought to be observed, that brewers' yeast will not answer the purpose.* To the malt and hops some add a little flour, but the patent yeast is quite as good without the flour, which in summer is apt to make the yeast go sour. By the above process five gallons of very good yeast may be made, which will be ready for use the day after it is made. It occupies in manu facturing from about seven o'clock in the morning till two or three in the afternoon; but it gives very little trouble to the baker.

* If this be the case, it may be fairly asked, by what means the first patent yeast was generated? The answer is, by a chemical process similar to that invented by Mr. Henry, and which we nave given under the head of Artificial Yeast.