986 Transactions of the American Institute. 



does not become deteriorated by use. A spring does part of the 

 work, and the mercury the rest. Tlie mercury is put in the cliamber, 

 and as the pressure acts upon the diaphragm, tlie mercury is forced 

 up in tlie glass tube, and the scale on the guard of the tube will indi- 

 cate the amount of pressure. 



Mr. C. E. Emery said that this gauge was almost exclusively used 

 on the boilers at the late fair. It gave much satisfaction, and pos- 

 sesses the advantage of the mercury gauge without the disadvantage 

 of the spring gauge. The range of the pressure is never beyond the 

 elasticity of the diaphragm. This matter of corrosion has been the 

 difficulty with all other diaphragm gauges, which the nickle plating 

 obviates. This instrument has to be placed in the engine room, 

 where the temperature is always about the same, and there adjusted 

 at zero. 



Dr. D. D. Parmelee said that the coating of the steel plate with 

 iiickle was a highly important improvement. 



The Chairman remarked that the nickle plating was the only 

 point of improvement in this gauge. 



Steam Boilers. 



Mr. J. K. Fisher read the following paper on the best form of 

 steam boilers : 



"Since the introduction of the multiflue boiler, in 1S29, and the 

 water-tube safety-boilers about the same time, there have been such 

 changes of proportion as have prevented the generation of dry steam 

 in most boilers. Tw^o of these changes are in the proportion of 

 steam room, and in the proportion of water-level, to the volume of 

 steam produced. Watt's proportion, for large boilers, was about one 

 cubic foot of steam room for 300 feet of steam made per hour. A 

 common proportion now adopted in locomotives is one foot of room 

 •for 900 feet of steam per hour ; and there are 'boilers of other kinds 

 in which the steam room is much less ; and this excess of volume is 

 aggravated by greater density — nine or ten times greater than Watt 

 used. In steam so dense, particles of water will not fall so rapidly 

 as they do in steam of one atmosphere, or a little less, such as AVatt 

 used. These changes have been made in consequence of a demand 

 for lightness and compactness, and not in consequence of careful 

 trials to arrive at the proportions necessary to make dry steam. On 

 the other hand, Watt disincumbered himself of all that stood in his 

 way, and planned his boilers strictly with a view to make steam per- 



