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Description of an Improved Frost Stop-Cock invented by Mr ALEXANDER M'EWAN PETERS, Plumber, Dundas Street, Edinburgh.*

This stop-cock is proposed to be placed on main-pipes for supplying cisterns, and is intended to obviate the great risk of such pipes bursting during protracted frosty weather. For this purpose the cock is furnished with two waterways, the one being used for the ordinary filling of the cistern from the reservoir or main conduit, whilst the other is employed for emptying that portion of the main pipe which lies between the stop-cock and the cistern, and which is, from its situation, especially exposed to the dangerous action of the frost. By

Fig. 1.

the arrangement of the stop-cock, this emptying takes place whenever the main supply is turned off; or, in other words, when the cock is shut. The key of the stop-cock is hollow, with a square tube for filling the cistern, as represented at E, figs. 1 and 2. In the former, the stop-cock is shown open, as it stands during the flow of the water from the main by the pipe A A to the cistern. On the side of the key is the aperture F (fig. 1), for the return of the water when the cock is shut. In fig. 2 the stop-cock is shown with the water returning from the upper portion of the pipe A, communicating with the cistern, round the square tube E, by the space D, and escaping through the exit-tube B, which may either be attached to a soil-pipe, or the water may be allowed to flow into a pail, or other suitable vessel placed to receive it. The stop-cock has an iron lever

* Read before the Society, and stop-cock exhibited, on 13th Feb. 1860.

C (fig. 2) attached to it as a handle, the short end of which points to the open or shut, according as the water is passing through the pipe at the time.

On Baking Bread, with an especial reference to German Yeast. By Mr JOHN MACKAY, F.R.S.S.A., Pharmaceutical Chemist, Edinburgh.*

Very early in the history of the world, and long before any professed baker was known, lentil, or flour of other grains, was mixed with water, made into a thick paste or mass, and hardened either by the heat of the sun or by that of a fire. While such a process would doubtless render the product useful and convenient, mankind in course of time discovered an improved mode of manufacture by the employment of a substance even yet well known to us-viz., leaven. Now,

not only in the use of this article, but in all subsequent attempts at improvements in manufacturing bread, the great object has ever been to produce, by certain chemical agents and changes, elimination of carbonic acid gas, which by its inherent elasticity and endeavour to escape slowly from the mass of dough, would cause such a separation of the particles of flour, that what might otherwise be a comparatively tough, firm, insipid mass, should be converted into a light, pleasant, agreeable, sweet loaf, easily masticated, and as easily digested. The leaven of which we read in the Bible was supposed to be made, as it still can be, and is, by keeping a quantity of flour and water at a certain temperature for a given time, and carrying on the process by gradually adding more flour and water, until, as the change proceeded, we had the true exemplification of a little leaven having leavened the whole lump. It was, however, ultimately discovered that a more rapid and better mode of arriving at the same result consisted in the use of brewing yeast, and for a long time it was regularly employed; and many a tramp some of our forefathers had in quest of this material when public brewing was in its infancy. Since then barm-breweries have been freely established, and baker's yeast is now regularly supplied in any quantity, and at a moderate charge.

A very proper inquiry might here be made, What is yeast or barm; and how does this substance act in producing such changes as those already referred to? To understand this thoroughly, we must for a moment consider the process of malting. When barley is steeped in water till it is softened and begins to swell, and then allowed to lie in heaps for a certain time, germination or sprouting takes place, during which it gives out a peculiar substance called diastase, possessing the power of converting the starch of the grain into sugar, and giving, to a very considerable extent, a similar power to other cereals. Its potency may be better comprehended when I mention, that five cwt. of malt is supposed not to contain more than one pound of diastase, but then it is believed that this quantity will convert nearly a ton of starch into sugar at a temperature of 150° F. That the analogy between leaven and yeast may not be lost sight of, I may state, that the gluten of flour,

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present, of course, in its natural state, in all grain, acts under heat and moisture, in a similar manner to the above substance diastase. The brewer and distiller having infused their malt and grain, produce a fluid more or less rich in saccharine matter, and this is run into suitable vats to undergo fermentation, which is done by adding a little fresh yeast kept from some previous making. A peculiar chemical action soon commences, and the fermentative process, or the conversion of the sugar into alcohol and carbonic acid, is soon completed. Now, the insoluble, yellowish, viscid matter, rising to the top in making beer or wash for the distiller, is what is known as yeast or barm, and for a certain time, and under certain circumstances, it retains the power of inducing the same action when mixed with flour and water, as well as in other cases where sugar is present.

The fermentation requisite to produce bread has been called panary, but this is a mistake, as it would lead one to believe that it differed from the vinous, which has just been shortly noticed. Such is not the fact, bread fermentation being precisely the same as that previously stated, but not carried to so great a length; or, in other words, the vinous fermentation was begun, and stopped long ere it was completed, by the heat of the oven. A natural inference will at once be drawn: if the process be the same, even for a time, then, as a consequence, a certain quantity of alcohol must be formed in making bread; and such is really the case. No one need however be startled at this statement, because all the spirit escapes in the form of vapour. A reference also to the chemical composition of sugar and alcohol will render the fact less surprising, because the former is composed of the very elements requisite to form the latter-namely, carbon, oxygen, and hydrogen and by such transformation give out not only alcohol in vapour, but also an abundant supply of carbonic acid to separate the particles of the flour. That such a change is neither theory or supposition, was most satisfactorily proved by Mr Graham so far back as 1826, who really obtained spirit from bread while in the oven. This he did in a very complete manner by baking bread with leaven, thus avoiding the least chance of spirit being present in the yeast, which might have

been alleged had he drawn the barm from a brewery. When the loaf was kneaded, he put it into a distilling apparatus, and kept the whole at a baking temperature for some time. The result was, that the condensed vapour gave a liquid having the taste and smell of alcohol; while, by repeatedly rectifying, a small quantity was obtained of strength sufficient to ignite gunpowder.

The experiment was variously repeated, and a calculation made, that every hundred parts of flour used, gave one part of alcohol. Proceeding on such basis, it has been estimated that from the quantity of bread annually consumed in London alone, no less than 300,000 gallons of proof spirit might be saved, were any means discovered by which the vapour could be collected and condensed. Mr Odling states that some years ago attempts of a very costly kind were made at the military bakeries at Chelsea with this object in view, and about L.20,000 were expended in the vain attempt to collect and secure the spirit thus given off.

It will therefore be seen, fermentation is absolutely requisite to produce good bread, and that, by certain chemical changes during the fermentation, a portion of starch is converted into sugar, which is again converted partially into alcohol and carbonic acid gas-the former escaping, the latter, from the heat of the oven, raising the loaf in consequence of its expansion and endeavours to escape. In making the dough. it is important that the baker should know the precise point at which to stop the process, which the action of heat enables him to do; for if unattended to, the vinous very rapidly passes under certain circumstances into the acetous stage, and the consequence would be unpalatable bread.

Ordinary brewers' yeast does not answer well for breadbaking from its extreme bitterness. Barm-breweries prepare daily supplies for bakers, and this they do by infusing malt, and inducing the fermentative action by the use of fresh yeast. Another kind of barm used by some bakers is Patent Parisian Barm. This is generally made on the premises, by infusing malt in boiling water, adding a small proportion of weak decoction of hops, mixing this at 212° Fahr. with some flour, adding all together, and setting aside for eight or ten hours