350 TRANSACTIONS OF THE AMERICAN INSTITUTE. I 



Mr. Seely.— Where oil is homogeneous the hydrometer is a good test, 

 but, since the manufacturers have mixed oils, it is not reliable. 



Dr. Stevens. — I think it important to have an instrument to test all oils 

 offered in market, whether on store or for sale. Lives should not be jeopar-jj 

 dized from mere ignorance, carelessness, or sheer cupidity. 1 have known' 

 a valuable life lost, the head of a family, dependent upon him for support, 

 by drawing from a barrel of explosive compound sold from this city. 

 When lives are lost from neio causes, there is always a season of great 

 excitement; there has recently been an increase of this from a few cases 

 of death from explosive vapor arising from petroleum oils, while the far 

 greater number of deaths arising from the use of burning fluid was for- 

 gotten. As to the temperature at which an explosive mixture will take 

 place, the compound of air and vapor will take place at low temperatures, 

 when the'l^apor is derived fresh from the bowels of the earth. At the 

 burning springs of New York and Ohio, this mixture takes place at the 

 common temperature of the air; at all seasons when the springs, flow, 

 spring, autumn, or summer, beautiful pyrotechnic exhibitions are then 

 gotten up extemporaneously. 



The subject of the evening, " Superheated Steam," being called up, Mr. 

 Babcock said: I know an instance in which superheated steam had been in 

 use six years, and saved 25 per cent., and the apparatus cost nothing for 

 repairs. It is automatic. The invention is by Wilcox Stillman. The 

 steam passes through a set of tubes; the smoke and heat cross these 

 tubes several times; between the fire box and chimney is a damper to regu- 

 late the quantity of smoke and heat which pass over the tubes; the 

 pressure is 50 lbs., condensing 100''; temperature of steam 450°, 



Prof. Seely. — The heat used in superheating is commonly waste heat, or 

 the heat going up the flues, in the products of combustion. Such heat 

 makes no extra cost, and all that gets into the steam shows itself in 

 mechanical force. The heat, however, which gets into the water in the 

 boiler is not all available in work; until the water reaches the boiling 

 point, the expansion, although of great force, is of such narrow limits that 

 we do not use it. To raise water from 0° to 212°, 20 per cent, as much 

 heat is required as to raise it then into steam; and this 20 per cent, gives 

 no motion to the engine. 



But the value of superheating is more plainly shown in another direc- 

 tion, and by using figures. In order to be easily understood, I use only 

 round numbers, but numbers which are very near the exact truth: 1 lb. of 

 water at 212° is converted into 1,100 volumes of steam, by 1,000 units of 

 heat. The 1,100 volumes may be taken as the measure of the available 

 mechanical force; the 1,000 units of heat are worth 1,100. Now, if these 

 1,100 volumes of steam at 212° be raised 500° higher, or to 112°, the bulk 

 will be doubled; for the heat put into the steam we have another 1,100 

 volumes; or, in other words, the heat used upon the steam has given us 

 the same value as the heat used upon the water. How much heat is there 

 required to raise 1 lb. of steam 500°? The specific heat of water is 1, and 

 the specific heat of steam .5, or a unit of heat will raise 1 lb. of water 1°, 

 and 1 lb. of steam 2°. But in our case, suppose the steam was raised 

 500°, and now it is evident at a cost of 250 units of heat. The 250 units of 



