BREAD 



491 



batch will take up 47 minutes. But on account of accidental interruptions, an hour 

 may bo assigned for each charge of 260 loaves of 1 kilogramme each ; being at the 

 rate of 6,240 kilogrammes (or 6'75 tons) of bread in 24 hours. 



Although the outer parts of the loaves be exposed to the radiation of the walls, 

 heated to 280 or 300 C., and undergo therefore that kind of caramelisation (charring) 

 which produces the colour, the taste, and the other special characters of the crust, yet 

 the inner substance of the loaves, or the crumb, never attains to nearly so high a tem- 

 perature ; for a thermometer, -whose bulb is inserted into the heart of a loaf, does not 

 indicate more than 100 C. (213 F.) 



Perkins* hot-water oven is an adaptation of that distinguished engineer's stove, 

 which, as is well known, is a mode of heating by means of pipes full of water, and 

 hermetically closed ; but with a sufficient space for the expansion of the water in the 

 pipes. As a means of warming buildings, the invention has already produced the 

 very beneflcal effects which have gained for it an extensive patronage. There is 

 no doubt but that this novel application entitles the inventor to the warmest thanks 

 of the public. The following figure (229), represents one of these ovens. A, stove; 

 B, coil of iron pipe placed in the stove ; c c, flow-pipe ; D, expansive tube ; E, oven 

 charged with loaves, and surrounded with the hot-water pipes ; F, return hot-water 

 pipe ; G, door of the oven ; H, flue for the escape of the vapours in the oven ; i, rigid 

 bar of iron supporting the regulating box ; j J, regulating box, containing three 



small levers ; K, nut adjusted so that if temperature of the hot-water pipe is increased 

 beyond the adjusted point, its elongation causes the nut to bear upon the levers in 

 the box J, which levers, lifting the straight rod L, shut the damper M of the stove ; N 

 is an index indicating the temperature of the hot-water pipes. 



The oven is first built in the ordinary manner of sound brickwork, made very 

 thick in order to retain the heat. Then the top and bottom of the internal surfaces 

 are lined with wrought-iron pipes of one inch external diameter, and five-eighths of an 

 inch internal diameter, and their surface amounts in the aggregate, to the whole 

 surface of the oven. These pipes are then connected to a coil in a furnace outside 

 the oven. The coil having such a relative proportion of surface to that which is in 

 the oven, that the pipes may be raised to a temperature of 550 F., and no more. 

 This fixed and uniform temperature is maintained by a self-regulating adjustment 

 peculiar to this furnace, which works with great precision, and which cannot get out 

 of order, since it depends upon the expansion of the upper ascending pipe close to the 

 furnace acting upon three levers connected with the damper which regulates the 

 draught The movable nut at the bottom of that expanding pipe being adjusted to 

 the requisite temperature, that precise temperature is uniformly retained. The 

 smallest fluctuation in the heat of the water which circulates in the pipes instantly 

 sets the levers in motion, and the expansion of one thirty-sixth part of an inch is 

 sufficient to close the damper. 



It will be observed that if the pipes be heated to 550 F. the brickwork will soon 

 attain the same temperature, or nearly so, and accordingly the oven will thus possess 

 double the amount of the heating surface of ordinary ovens applicable to baking. 



