During the past few weeks, a highly interesting experiment--and one, moreover, destined to materially influence the development of the uses of gas in a fresh field--has been in progress, under the guidance of Mr. Booer, at a baker's shop in the Blackfriars Road, London. The experiment in question is nothing less than the application of gas for heating bakers' ovens, in a manner not hitherto attempted, and such as to bring the system within the means of the poorest tradesman in all but the smallest towns. It will be remembered that the success of the gas-heated muffles for burning tiles and glass led to the attempted construction of a model baker's oven, heated by the same fuel, which was shown in action at the Smoke Abatement Exhibition at South Kensington in the winter of 1881-82. This model attained considerable success; but its design demanded either a new structure in every case, or considerable alteration of any existing oven. In the proposed system, moreover, the oven was heated wholly from without--a condition supposed to be necessary to meet the objections of the bakers.
It is evident, however, that there must be considerable waste of gas in heating a mass of tiles and brickwork, such as go to the construction of a common baker's oven, from the outside; and the objection to handicapping such a costly fuel as gas in this manner becomes more apparent when it is remembered that in the usual way the oven is always heated by an internal coal fire. When it is further considered that the coal commonly used by bakers is of the most ordinary quality, full of dirt that would condemn it in the estimation of a gas manager, the sentimental objection to allowing a purified gas flame to burn in a place which this rubbish is permitted to fill with foul smoke becomes supremely ridiculous. Consequently, when Mr. Booer, whose work in connection with the gas muffle is well known in England and America, seriously addressed himself to construct, upon altogether new lines, a cheap and practical baker's oven, he wisely put the gas inside.
There are many other conditions which Mr. Booer, after consultation with practical bakers and others, set himself to fulfill, the observance of which lends to the present Blackfriars experiment much of its interesting character. Thus it was observed that, while it is not difficult to build an oven in a given spot, and bake bread in it, this cannot truly be called a baker's oven. By this term must be understood in particular an oven in an ordinary bakehouse, set in the usual style and worked by a man with his living to get by it. Before the problem of extending gas to bakers' ovens could be considered solved, it had to be attacked from this aspect. Mr. Booer, to do him full credit, seems to have early appreciated this fact in all its bearings. He not only saw that it was necessary to save gas, as much as possible, by putting it inside the oven; but he was told that, in order to meet with any general success, the cost of converting an oven to the gas system must be rigidly kept down to about ten or twelve guineas. The latter seems a particularly hard condition, when it is remembered that the only improved baker's oven in practical use at the present day is the steam oven invented by Mr. Perkins, which costs two or three hundred pounds to erect.
Mr. Booer also had in mind the necessity that everything possible for a coal oven must likewise be performed by a gas oven; and in this respect he set himself to surpass the costly Perkins oven, which will not bake the common "batch" or household bread, generally the principal article of sale, more especially in populous and poor neighborhoods. The peculiar efficacy of the common coal fire in this respect proceeds from the essential principle of action of a brick oven, which is found simply in the fact that the work is done entirely by heat previously imparted to the tile bottom, roof, and sides of the oven, and thence radiated to the bread. No other kind of heat will bake batch-bread--i.e., loaves packed in contact with one another--which requires to be thoroughly soaked by a radiant heat in a close atmosphere of its own steam. Now, as a coal fire is eminently qualified to impart, by radiation and otherwise, this necessary store of heat to the brickwork, it is plainly a difficulty to effect the same purpose with a fuel which, of itself, can scarcely radiate heat at all.
The system of the gas cooking-oven--the utilization of the heat of the combustion products as formed--is clearly inapplicable here; for a different kind of heat is needed, under conditions that would not sustain continuous combustion. Therefore, there is nothing for it but to heat the bottom and sides of the brick oven by the direct contact of powerful gas-flames; thus supplanting the coal fire, but leaving the actual work of baking to be done afterward by stored-up heat in the regular way.
Having settled the general principles of a system of this kind, there still remain a number of scarcely less important details, in the dealing with which lies the difference between practical success and failure. Thus it is not merely sufficient to heat an oven for bread baking; it is also necessary to heat it within the times and according to the habits of work to which the baker has been accustomed. Work in town bakeries begins at about midnight, or shortly after, and the condition of the oven must conform to the requirements of the dough, which vary from day to day and from season to season. In order to master all these niceties, as far as a knowledge of them is necessary to his purpose, Mr. Booer has spent many nights in the bakehouse in the Blackfriars Road; and has thereby obtained a command over the technicalities of the work which has served him in good stead, not merely for adjusting his gas heat, but in answering the innumerable objections always raised when a revolution in an immemorial trade is threatened.
It is with considerable satisfaction that we are enabled to declare, after duly weighing all the conditions as to first cost and otherwise imposed by himself and others, that Mr. Booer has succeeded, upon these terms, in vindicating the claims of gas to be a cheap, efficient, and cleanly fuel for heating ovens under the control and according to the methods of working of the baker himself.
The oven with which this success has been achieved is one of two in the bakehouse of Mr. Loeber, of 161 Blackfriars Road. It measures 7 feet by 6 feet internally; being what is technically termed a 6 bushel oven. The alterations made by Mr. Booer consist in the first place in the removal of the flooring tiles, and the laying down of a new bottom, under which run a number of flues radiating from the side furnace. The throat of the furnace, where it enters the angle of the oven, is bricked up, and eight pieces of ¾-inch gun-barrel tubing project above this dwarf wall, and radiate fan-shaped under the dome of the roof. These are the gas-burners, which are supplied from a 1½-inch pipe led into the old furnace. The same pipe supplies the similar burners which are inserted in the flues under the oven bottom. This is really all the plant required. It should be remarked that these bottom flues are carried to different points of the side walls, and the products of combustion are allowed to rise upward into the oven through gaps left for the purpose. A supplementary supply of heated air is provided to help the combustion of the gas in these flues, which would otherwise be languid.
When the gas is turned on from the main cock in the furnace either to the top or the bottom set of burners, a long match is used to light them from the same point. This is effected without risk of firing back, by the adoption of a specially constructed atmospheric nipple and shield, the pattern of which is registered. The flame from the top burners unites in a sheet of fire, which spreads out all over the crown of the oven, at the same time that the burners below are doing their work, and the products of combustion flow together through the oven to the chimney, which is the same that was used for coal. At first, as might be expected, there was considerable difficulty in finding the most suitable position of the chimney damper, aggravated in this case by the fact that the other oven worked with a coal fire into the same shaft. Finally, however, the two flues were disconnected with the happiest results. During the past fortnight the oven has been in regular use, and the bread has been sold over the counter in the ordinary course of trade. Two and three batches of bread have been baked in one day in this oven; the economy of its use, of course, increasing with the number of loaves turned out.
As a rule the gas is lighted for about an hour before the oven is wanted, and about 250 cubic feet are used. Then the cocks are shut and the oven is allowed to stand closed up for ten minutes, in which time it ventilates itself, and the heat spreads over it. Then the batch is set, and the baking occupies from an hour to an hour and a half, according to the different classes of loaves. Two batches are baked with a consumption of about 620 cubic feet of gas; costing, at 2s. 10d. per 1000 cubic feet, just 11d. each batch for fuel. This cannot be considered costly. But the system possesses many other advantages. In the first place, it is much more cleanly than coal; for the oven never requires wiping out, which is usually done with a bundle of old rope called a "scuffle" and the operation is attended with a most unpleasant odor. Then there is no smoke--a great advantage from the point of view of the Smoke Abatement Institution. More to the purpose of the journeyman baker, however, is the fact that there is no stoking to be done, and he can therefore take his repose at night without having to attend to the furnace.
Besides this the master has the satisfaction of knowing that the oven will always be hot enough if he simply attends to the time of lighting the gas--a consideration of no small moment. It is no mean testimony to the reality of Mr. Booer's success that Mr. Loeber, having seen his difficulties and troubles from the beginning, and marked how they have been overcome, is content to acknowledge that even this first example is capable of turning out bread in a condition to be sold over the counter. There is a good opening in this direction, for there are 6,000 bakeries in London alone, to every one of which Mr. Booer's system might be applied with advantage to the tradesman and his customers. And what may be done with gas at about 3s. per 1,000 cubic feet may certainly be done to still greater advantage in many towns where the price is lower. Mr. Booer has entered upon his work in a proper spirit. He has begun at the beginning, with the necessities of the baker; and has gone plodding on quietly, until he has achieved a noteworthy success.
It may be hoped he will receive the reward which his perseverance merits.--Jour. of Gas Lighting.