others under the impression that by giving a portion of this article away, they might be retarding, or even preventing the entire conversion of the sugar into spirit. On every side I met a civil but decided refusal.

I have never, however, lost sight of any chance I had of repeating my application, and as there is at the present time a decided feeling, to lessen restrictive interference in all branches of trade, wherever this can be safely and wisely done, I lately found liberal minded parties, who were disposed to give me the opportunity I had so long sought, that of experimenting upon distillers' yeast. After numerous trials, I have now to announce, that I have been quite successful in manufacturing a solid yeast, in every respect equal to the German. I claim, therefore, the position of having been the first to produce such an article in this country; and that the statement might be borne out by practical proof, I have had my preparation tested side by side with that imported from Holland, and the operation has been in every respect equal. By this I mean a similar quantity of my prepared yeast and that imported, produced the same effect on a given quantity of flour, water, and salt, and in the same time. Of course it was tested in this manner by regular bakers, whose daily employment consists in baking bread. Samples have also been tried in confectionary establishments and found to answer remarkably well for fancy bread of different kinds. So far, therefore, as the various SAMPLES have been tried, my success has been complete, and beyond even my own expectations.

But already I hear it questioned, Why introduce this substance to the notice either of the trade or the public, while it is known that the existing Excise Laws are such as to prevent any distiller furnishing supplies of his yeast? To this I reply, distillers have long felt they have been unfairly treated, in not being allowed to use a portion of their own yeast for succeeding operations in their fermenting vats, and more than one application has been made to the Board of Inland Revenue for remission of such a law. The hardship of this regulation may be better understood, when I mention, that it costs the distiller, according to the size of his work, hundreds or thousands 2 G

VOL. V.

of pounds annually, for brewer's yeast to assist in the required fermentation.

From a very recent application to the Chancellor of the Exchequer, it is uncertain whether permission will be given to the distiller to use his own yeast, but there is every prospect, I may say certainty, from the feeling displayed, that there will be immediate removal of the present prohibition against the use of this article for baking purposes. Thus the manufacture of dried yeast in this country may ere long become a very important one, and I hope soon, from arrangements which are now being made, to be able to supply this article, fresh and in good condition, to all who may wish to try its capabilities in plain and fancy baking. The value of German yeast in some districts in England would create surprise here. Some even in Edinburgh are alive to its importance; for only last summer three parties joined in the attempt to get regular supplies into Leith, but failed; whether from careless shipping, or from the heat of the steamer, was not proved, but the yeast frequently arrived quite putrid and unfit for use.

Before closing these remarks I may shortly refer to the principal advantages said to be possessed by the German over any ordinary baking barm. Of course the steady and large consumption of German yeast throughout England, which has been already referred to, is a proof that all who have fairly tried it there, for baking purposes, consider it superior to any other ferment. This applies partly to professed bakers and confectioners, but especially to private families. One great superiority consists in the rapidity with which panary fermentation is completed. Some bakers who set what is called a quarter sponge, require 16 hours to elapse before the bread is ready for the oven. The general average may however be assumed as 12 or 13 hours. Now, bread has been made ready for the oven by samples of the German yeast, made by me, in as short a time as 1 hour-generally 2-and never exceeding 23, unless wished to extend over a longer period for the purpose of making a small quantity of yeast go a greater length. Thus there is a great saving of time when compared with the ordinary process of bread-making. Again, both baker and confectioner may have now and then a greater demand than

they calculated upon, and from the long time required to make their dough, must disappoint many. In such cases the German yeast would be most useful. Bakers and private families in small villages, the inmates of noblemen's mansions, and other places in the country, might also bake their own bread by the use of such an article. But the bread so baked is thought to be sweeter and better than ordinary bread, and is said to keep so for a much longer time than that usually sold. In the hands of practical men these advantages might be much extended; and as, up to the present time, there have been difficulties in the way of procuring supplies of German yeast for Scotland, the baker must by experience satisfy himself whether the character of this article has been generally over-estimated or not.

I have tried in vain to reduce the German yeast to a state of powder. Heat or warmth, however slowly applied, seems to destroy in a great measure its vitality, which no subsequent nursing can restore. This need scarcely excite surprise; for doubtless had there been a possibility of so preparing it, the Germans would have long ago adopted this, by far, more portable and convenient mode of sending it across here, than the usual system of coarse canvass bags in use up to the present time. In speaking thus, it must not be supposed that I refer to the baking-powders now so common-some of which bear the name of German yeast-for baking bread, &c. These are all artificial, and generally composed of alkaline carbonates and vegetable acids, so prepared as to keep undecomposed until brought under the influence of moisture, when there is an immediate elimination of carbonic acid gas.

I do not think any means can be devised to keep German yeast beyond a certain time. During the coldest weather I found my best samples keep good for 17 days; but as the weather got a little milder they began to give way generally about the tenth day. Of course in summer weather the time will be still shorter. In fact, throughout the whole of the manipulation I found the greatest care requisite, as very little rough usage will go far to injure, and even destroy, the fermenting properties of the yeast.

Description of a Self-Acting Air Trap-Door for Mines. Constructed by Mr JOHN GEMMEL, Manager of Galston Colliery in Ayrshire. Communicated by D. LANDALE, M.E. *

In fiery collieries the trap-door forms a most important implement, as by it the several currents of air are kept in their proper circuit.

The neglect of trap-doors, by being left open, stops the stream of fresh air, and all the mine inside of them is liable to be so contaminated with fire-damp as to reach the point of explosion, and many of the sad accidents in mines which we continually read of in the newspapers can be traced to the neglect or improper placing of air-crossings and trap-doors.

In all particular doors in mines which give off gas, it has been the custom to station boys of from ten to fourteen years of age, who are paid from 10d. to 1s. per day to open and shut them as the drawers pass and repass with the full and empty tubs, and it is no uncommon thing for such doors to be opened and shut 500 and 600 times a-day. There are places of importance, however, where the traffic is limited, and the keeping of these is a dreary occupation for the poor boy, who often sits alone in the dark for hours (in order to save lampoil); in such cases, the temptation to leave his post and seek society where the men are working is strong, and often yielded to; whilst in the meantime some reckless drawer may pass and leave the door open, and thus produce an explosion.

Many devices have been tried to make a trustworthy selfacting door that will shut of itself without trouble to the passing drawers, for if it give them the smallest amount of trouble, when the throng and the heat of the day's work comes on, it will likely be propped open and left so.

Any mechanism applied must also be of the simplest character, and not liable to derangement from any movement of the roof or heaving of the pavements, circumstances quite common to thin coals and ironstones, which are worked longwall.

There must be no fine work either, such as the finely hung

* Read before the Society, and model exhibited in action, 26th March 1860.

doors to shut of themselves, which we see in our banks and public offices, opening either way to the passengers.

They must be stout, sturdy doors to shut firm and tight into their checks-air-tight, and fit to bear the blow of a tub coming at six miles an hour.

Mr Gemmel's door is sketched in the woodcut, along with

b

H

Fig. 1.

a piece of the railway and a tub. The door A (fig. 1.) is fitted into a stout frame, and strongly hung off the plumb, so that it may fall, shut of itself, into its checks, and being placed against the current, the blast of air assists to shut it quickly. So far, then, the door is self-acting one way, owing to the manner in which it is placed and hung.

The empty tubs from the pit bottom, going to the wall faces, strike the buffer-spring b (which saves the door. from the blow), it thus flies open and shuts of itself.

For the opening of the door from off the inside, a malleable

iron bell crank C is

Fig. 2.

placed on an upright spindle d (fig. 2), hung between two props, e and f, and made to stand across the mine-a chain