PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 315 



atom of oxyg^en, forming- carbonic acid g-as. According to the experiments 

 of Dulong-, Despretz, and Iless, tlie quantity of heat developed is precisely 

 the same, whether the carbon is converted into carbonic acid at once, or bj'^ 

 the intervention of carbonic oxide. In the table given, the heat developed 

 by burning carbonic oxide is apparently too low, but it must be borne in 

 mind that the amount of carbon employed is only six-lourteenths' of the 

 weight of thivS fuel. 



Mr. Garvey spoke of the constJinption of fuel in marine boilers, and the 

 waste resulting from the excessive stirring of the fires, by which valuable 

 uncombined products are carried off by the strong- draft. 



In the course of the evening, J. Wyatt Reid called attention to some cal- 

 culations he had made in relation to the use of steam cxpaiisively. As the 

 subject is one of general interest, it was decided to discuss it at the next 

 meeting. 



Adjourned to May 26. 



Americ.\n Institute Folytecitxic Association, ) 



May 26, 1864. ) 



Chairman, Prof. S. D. Tillman; Secrctaiy, Mr. B. Garvey, 



Screw-Threads and Bolts. 



It is now the practice of each manufactory in this country to follow its 

 own patterns without any reference to those of other establishments. The 

 evils growing out of a want of uniform system are numerous. The most 

 serious attend the repairing of machinery when the orig'inal patterns of the 

 screws used cannot be obtained. The following extracts from an able com- 

 munication lately made to the Franklin Institute, of Philadelphia, by Wm. 

 Sellers, were read: 



"The importance of a uniform system of screw-threads and nuts is so 

 generally acknowledged by the engineering profession, that it needs no 

 arguments to set forth its advantages; and in offering any plan for their 

 acceptance it remains only to demonstrate its practicability and its supe- 

 riority over any of the numerous proportions now used by the different 

 manufacturers. In this country, no organized attempt has yet been made 

 to establish any system, each manufacturer having adopted whatever his 

 judgment may have dictated as the best, or the most convenient for him- 

 self; but the importance of the works now in progress, and the extent to 

 which manufacturing has attained, admonish us that so radical a defect 

 should be allowed to exist no longer. The importance of this subject was 

 long ago recognized in England, and the engineers of that country, by 

 mutual agreement, adopted the proportions now in universal u'^e there. 

 Our standard of length being the same as theirs, it would seem desirable 

 that the system wfiich they have adopted shcnild also be employed by us, 

 unless grave objections can be urged against it, and a better one substi- 

 tuted. The form of curve adopted by the English engineers is one with 

 flat sides at an angle with each other of 55 deg., with a rounded top and 

 bottom. The proportions for the rounded top and bottom are obtained by 

 dividing the depth of a sharp thread having sides at an angle of 55 deg., 



