TRANSACTIONS OF SECTION I!. 495 



8. Metallic Compounds containing Bivalent Hydrocarbon Radicals. Part III. 

 By Professor Sakueai, F.C.S. 



By acting on mononiercuric methylene iodide, PIgCHjIo — tlie preparation of 

 ■which is described in the Report, 1880, p. 504 — with mercuric cliloride, a com- 

 pound is obtained which is shown to be monomercuric methylene chloriodide, 

 IIg(0H2)"ClI. This compound is soluble in ether, chloroform, and alcohol, and 

 crystallises in thin shining white plates, m.-p. 129°. The action of iodine on this 

 compomid shows it to be constituted thus : ClCILIIgl, inasmuch as it is thereby 

 converted into mercimc iodide and methylene chloriodide, thus : C1CH„ Ilgl 



ii 



Methylene chloriodide, CHjClI, is a liquid boiling at 109°, and having a specific 

 gravity of 2'49 at 20° C. The boiling point of this compound is the mean of the 

 boiling points of methylene chloride and methylene iodide. 



SATURDAY, AUGUST 26. 

 The Section did not meet. 



MONDAY, AUGUST 28. 



The following Reports and Papers were read : — 

 1. Beport of the Committee on the Calihration of Mercurial Thermometirs. 



See Reports, p. 145. 



Third Report of the Committee upon the present state of our Knoivledge 

 of Spectrum Analysis. — See Reports, p. 120. 



3. On the Reversals of the Spectral Lines of Metals. By Professor Liveing, 

 F.'B.S., and Professor Dewar, F.R.S. 



The authors have made a regular study of this subject, not only with a view 

 to trace the parallel between the conditions of the elements as they exist in the 

 sun and those in which they can be placed on earth, but also because a knowledge 

 of the reversible lines may help to distinguish those due directly to the vibrations 

 of the molecides from those produced by superposition of waves or by some strain 

 upon the molecules, such as an electric discharge might give. They classify the 

 reversals as follows. I. Reversals where the expanded line itself gives the back- 

 ground against which the absorption line, narrowed because density of the ab- 

 sorbent is less than that of the'emittent vapoiu-, is seen. These are the reversals 

 most generally known. 11. Reversals in which there is little or no expansion of 

 the lines, and the background is either the hot walls and end of a tube, the hot pole 

 of the arc, or such part of the arc as is so full of lines as to be nearly continuous. 

 Many such reversals, including many lines of iron and other metals, were exhibited 

 in photographs. III. Reversals in which the background for the absorption was 

 produced by the expansion of a line of some other metal. Photographs of the 

 reversal of iron and other lines seen against the expanded magnesium^ lines were 

 exhibited. IV. Reversals by the introduction into the crucible in which the arc 

 was passing, of a very gentle current of hydrogen, coal-gas, or ammonia, by which 

 the metallic lines are almost all swept away, and the continuous spectrum much 

 increased. V. When a carbon tube, passed through a perforation in a block of 



