CRITICAL NOTICES OP NEW PUBLICATIONS. 319 



being, however, of the same form — disk valves. This form is stated 

 to have been selected as most applicable to practice, from the ease 

 with which the touching surfaces can be ground into contact, and the 

 impossibility of tightening by friction, as in the case of the cone. 

 The observed pressures at which the valve rose were uniformly below 

 the calculated pressures at which, allowing for the weight, leverage, 

 and friction, the valve would have been expected to rise ; the mean 

 ratio being as 1 to 1.035. In no case was any undue adhesion ob- 

 served. While these experiments are favourable to the use of the 

 safety-valve, when well constructed and kept in good order, they can- 

 not be considered as justifying that feeling which imagines a valve to 

 be a security, without inquiring into its condition. On the contrary, 

 we find in this Report a well-authenticated instance of great adhesion 

 of the valve to its seat, requiring, when the pressure of the steam was 

 above that which should have raised the valve, considerable force ap- 

 plied at the end of the lever to open it. 



Besides two safety valves, the regulations for the safety of the 

 steam engine, until lately in force in France, required that fusible 

 plates, or plugs, should be placed in or over an opening into the 

 boiler. These, giving way when the steam within reached the melt- 

 ing point of the alloy constituting the plate, allowed the escape of 

 steam. These plates were intended besides to apply to a case in 

 which the safety-valve is inoperative, namely, when, from a defici- 

 ency of water in the boiler, parts of the metal have become highly 

 heated, and thus have heated the steam above the temperature corres- 

 ponding to its density.* The experiments made on these plates were 

 numerous, and lead to a conclusion of considerable interest as afi'ect- 

 ing their use. It was found that the alloys composing the plates 

 soften, in part, before they reach the temperature of fusion of the 

 whole mass, and that liquid portions are forced out through the holes 

 of the brass plate which, in practice, covers them, leaving a less fu- 

 sible mass. In the case of one of the alloys, which melted above 



* That steam thus surcharged with heat may exist within a boiler which 

 yet contains some water, appears to have been generally assumed. The 

 fact was made the subject oi experiment by the Committee, who found it to 

 be as assumed. The steam was produced' and kept up by a charcoal fire 

 placed under a boiler, while a similar fire above the boiler surcharged with 

 heat the steam produced. The committee found that the elastic force of the 

 steam calculated on the supposition of its expanding by heat as a gas agreed 

 very nearly with the observed force, differing but .05 o'f an atmosphere at the 

 temperature of 533**. The thermometer giving the temperature of the wa- 

 ter in the boiler had become deranged during the course of this experiment 

 by an accident, but this close coincidence certainly rendered a repetition of 

 the inquiry unnecessary. On these experiments,' our good-natured cotem- 

 porary before referred to remarks; "The Sub-committee did not make 

 one experiment on this subject ; they decide upon the uncomfortable expe- 

 riments of the preceding investigation, &c." Which uncomfortable experi- 

 ments, as he facetiously (?) terms them, were quite as directly to the point 

 as if they had been intended solely to apply to it, to the exchision of all other 

 deductions. 



