1879.] On i\Jost General Problems in Continuous Beams. 



493 



"159 grm. gave 

 •165 



•170 „ 

 •180 „ 

 103 

 174 



Potassium Iodide. 



2075 at 0° and 760 mm. 



212 „ 



214 „ 



21-6 



151 



24-4 



Mol. wt. 



Mean molecular weight 



171 



174 

 177 

 186 

 152 

 159 



169-8 



These numbers are fairly accordant, and seem to indicate that 

 iodide of potassium is normal in its behaviour. The vapour, after 

 each experiment, was blown out with a current of hydrogen. A 

 crystalline deposit was obtained in each case, which was pure iodide 

 of potassium, free from any trace of iron. Taken in connexion with 

 the former experiments, this seems to show that, if free potassium is 

 abnormal, its compounds are not altered. Before any final con- 

 clusions can be reached, further experiments must be made in pla- 

 tinum or iridium vessels, and it will be very important to control 

 the results by examining the densities of the iodides of caesium and 

 rubidium. 



IV. " On the Practical Solution of the Most General Problems 

 in Continuous Beams." By John Perry and W. E. Ayrton. 

 Communicated by Fleeming Jenkin, F.R.S.S. Lond. and 

 Edim, Professor of Civil Engineering in the University of 

 Edinburgh. Received November 27, 1879. 



1. It is not necessary to enter into the question of the advisability 

 of employing continuous girders in bridges with spans of less than 

 200 feet, but it is generally conceded that the increased economy due 

 to the employment of continuous girders in longer spans more than 

 counterbalances the well-known practical objections to continuity. 

 Hence the practical solution of the general problem — given the con- 

 ditions at the ends of a continuous girder, the spans, the moment of 

 inertia of all cross sections, and the loading, to find the bending 

 moment and shearing stress in every cross- section, is not unworthy of 

 our attention. 



2. Mr. Heppel has published the exact solution for cases in which each 

 span may be supposed divided into two, three, four or five equal parts, in 

 each of which the load and cross-section are supposed to be constant. As 

 is well known, the difficulty of the general problem is due to the 

 necessity of making certain summations in each span. Xow, Mr. 



