482 NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, B.C., 



2946 Marcet's Apparatus, for showing the Temperature and Elastic force of High 



Pressure Steam, and the most important facts connected with Latent 

 Caloric (fig. 2946) price 440 



Marcet's Apparatus consists of a strong iron boiler, mounted on a tripod 

 stand, with a stout barometer tube of about 33 inches in length, and open at both 

 ends, passing through a stuffing box on the top of the boiler to within a short 

 distance of the bottom : attached to the tube is a scale divided into inches and 

 tenths; on one side of this tube is mounted a very accurate thermometer, and 

 on the opposite side is placed a stop -cock, to which can be attached tubes for 

 conducting the steam to any vessel or apparatus for experiment. 



When in use, about 8 ounces of mercury are poured into the boiler, which is 

 then half filled with water. By the application of heat the water is boiled with the 

 stop -cock open, from which will issue steam, and the temperature indicated by the 

 thermometer will be 212 degrees of Fahrenheit, when the barometer stands at 30 

 inches. Upon closing this stop-cock the pressure will be increased, and will 

 gradually force the mercury from the bottom of the boiler up the tube, until it 

 marks about thirty inches on the scale, the pressure being equal to one additional 

 atmosphere (15 Ibs.), and the temperature marked by the thermometer will be 

 250 Fahrenheit, showing the relation between pressure and temperature in the 

 formation of steam.* 



2947 Dr. Ure's Steam Apparatus, for demonstrating the 



same facts as Marcet's price 440 



2948 Benevides' Steam Apparatus (fig. *2948), shows a modified and larger form 

 of Marcet's Apparatus, contrived by Professor Benevides, of Lisbon, for exhibiting 

 in a lecture room or to a class the various properties of Steam. 



It consists of a strong boiler, B, and on the top of it are three stuffing boxes, 

 b, c, and d, with fittings for a thermometer, a barometer tube, and a mercurial 

 syphon pressure-gauge, all mounted with suitable scales. A model of Giffard's 

 injector, G, is also adapted to the boiler. At A is a stop-cock, for connecting any 

 piece of apparatus to be experimented with. Among many important facts to be 

 demonstrated by this apparatus is the amount of heat] rendered latent when any 

 given quantity of water is converted into steam and other phenomena of latent 

 heat the laws of ebullition, the influence of pressure over the boiling point of 

 water, the connection between temperature and the elastic force of steam, the 

 production of motion by the elastic force of steam, &c. The action of Giffard's 

 injector is also very prettily illustrated, a small jet of water being easily projected 

 12 ft. with a good pressure of steam. Fig. 2948, Price 5 10 



2948* " It is proved by experiment that the quantity of heat necessary to raise one 

 pound of water one degree "of Fahrenheit in temperature is equal to that generated 

 by a pound weight falling from a height of 772 feet against the earth. Conversely, 

 the amount of heat necessary to raise a pound of water one degree of temperature 

 would, if all applied mechanically, be competent to raise a pound weight 772 feet 

 high, or it would raise 772 pounds one foot high. The term 'foot-pound ' has been 

 introduced to express in a convenient way the lifting of one pound to the height of 

 a foot. Thus the quantity of heat necessary to raise, the temperature of a pound of 

 water one degree Fahrenheit being taken as a standard, 772 foot-pounds constitute 

 what is called the mechanical equivalent of heat. If the degrees be Centigrade, 1,390 

 foot-pounds constitute the equivalent." Tyndall. 



* See Dr. A. S. Taylor's Thermometric Table. 



