Scientific Lectures. 103 



great intensity, may be tlirown into tlie oven and reflected from tlie 

 smooth roof, to almost instantly redden a very thin crnst. The 

 cracker bakery is a highly heated trunk, through which an endless 

 metallic apron is made to carry a constantly renewed supply of cracker 

 dough. The baked crackers are as regularly discharged from one end 

 of the trunk as the fresh crackers in dough are introduced at the other. 



The Mechanical Bakery. 

 I will mention only one other invention in this direction. It 

 contemplates the baking of a sufficient amount of bread to supply a 

 city from a single establishment, and Avas the work of a man whose 

 name is familiar to you from eminent services in the art of war as 

 well as in the arts of peace, Mr. Hiram Berdan. He conceived the 

 idea of an oven which should produce all the loaves of uniform excel- 

 lence and with a rapidity before unheard of. His apparatus may be 

 described as consisting of two towers filled with heated air, in one of 

 which was an elevator always slowly ascending, and in the other a 

 similar contrivance always slowly descending. On these was arranged 

 a series of platforms with a few inches between, each platform, or 

 huge tray, containing a hundred loaves or more. As each platform 

 attained the summit in one tower it was shot across to the other 

 tower, in which it descended to the bottom and discharged itself. 

 As soon as it was discharged it was shot across to the foot of the 

 ascending tower and refilled witli loaves of dough to renew its course. 

 The time of ascending and descending was so arranged as to exactly 

 complete the baking. The whole series of movements of the platform 

 was automatic, and carried on by steam power. Several of these 

 grand ovens — the mechanical bakeries — were eonstruQted in our large 

 cities, and promised at one time to revolutionize the system of city 

 bread baking. Precisely why they did not succeed I do not know. 

 Some of them were destroyed by fire, under circumstances which led 

 the proprietors to think the fires were the work of incendiaries. The 

 establishment first erected in Boston upon the plan of !Mr. Berdan 

 was burned, and as an amateur I undertook to find out the cause. 

 I came to the conclusion that it was an instance of spontaneous 

 combustion, arising from the dripping of oil from an axle working in 

 highly heated space, and falling on a mass of heated sawdust. Such 

 cases are unfortunately not rare. Bales of woolen shawls, imperfectly 

 freed of the oil introduced in manufacture, have taken fire spontane- 

 ously. Piles of cotton-waste, cotton saturated with oil, and heaps 



