Proceedings of the Polytecmnic Association. 1015 



dnee a sudden change of volume ; and during this process it is easy 

 to distinguish, by optical characters, the carbonic acid which has 

 collapsed from that which has not changed its volume. But when 

 the same change is effected by the continuous process, the carbonic 

 acid passes through conditions which lie between the ordinary 

 gaseous and liquid states, and which we have no valid grounds for 

 referring to the one rather than to the other. ISTitrous oxyd, hydro- 

 chloric acid, ammonia, sulphuric ether, sulphide of carbon, all 

 exhibited critical points when exposed under pressure to the required 

 temperatures. The author proposes for the present arbitrary distinc- 

 tion between vapors and gases, to confine the term vapor to gaseous 

 bodies at temperatures below their critical points, and which, there- 

 fore, can be liquefied by jDressure, so that gas and liquid may exist in 

 the same vessel in the presence of one another. 



New E.0TAEY Dynamometer. 



Mr. John W. Sutton, of Oregon, presented a new dynamometer. 

 It consists of two discs connected by springs. One of these discs is 

 fastened upon the shaft, the other is made fast to the pulley which 

 takes the driving belt ; this pulley is loose upon tlie shaft and trans- 

 mits the power through the connecting springs. A graduated scale 

 with an index marks the number of foot-pounds, or, where the num- 

 ber of revolutions is known, the number of horse-power. Means 

 are also provided for automatically recording the amount of work 

 done, much the same as in the indicator diagram. Tliis instrument 

 could be applied to shafting of almost any size, and is capable of 

 measuring up to about fourteen horse-power. It can be adjusted, 

 and set at zero at any time, should the springs vary, AVliere it is 

 desirable to test the value of lubricating oils, part of the springs can 

 be removed, by which the instrument is made very delicate. The 

 instrument here shown had been running for six weeks at the fair in 

 San Francisco, and had also been at other places, 



Dr, Yanderweyde said that this instrument appeared to be better 

 than an}'- we have here, and is deserving of much more general use. 

 An article of this kind is wanted very much. Here in New York, 

 steam power is rented out, and a person using a saw which, he says, 

 will require so much horse-power, but the owner of the engine finds 

 that he burns much more coal than would be required according to 

 the estimate of the owner of the saw. Ilorse-power costs, in the 

 very best engines, two and a half pounds of coal per hour ; so if in, 



