428 



Mr. T. Davidson. On Brachiopoda. 



[May 23, 



Exper: 



iment I. 

 II. 



Temperature 

 determined 

 calorim etrically . 



859° .. 

 828° . . 



Specific gravity of 



the vapour of 

 tliallium chloride. 



. .. 8-15 



III 1015° 



IV. 

 Y. 

 YI. 

 VII. 



859° 

 1026° 

 852° 

 837° 



28 

 06 

 43 

 75 

 60 

 84 



The specific gravity of thallium chloride vapour calculated upon the 

 supposition that the molecular weight of the compound is 238*07, and 

 its formula T1C1, is 8*49. 



Four determinations of the specific gravity of mercury vapour made 

 simultaneously with four of the above experiments gave as a mean the 

 number 6*0 instead of 6*728. 



The specific gravity of the vapour of lead chloride was made in a 

 similar way, but the temperature required for complete volatilization 

 is much higher than that needed in the case of the last compound. 

 The residue left in the globes was completely soluble in hot water, and 

 contained lead and chlorine in the proportion of one atom of the 

 former to 2 "08 of the latter. 



Temperature Specific gravity of 



determined the vapour of 



calorimetrically. lead chloride. 



Experiment I. 1046° 9 \L2 



II 1089° 9 72 



III 1077° 9*51 



IY 1070° 9*64 



The specific gravity calculated from the formula PbCl 2 =277 , 14 is 

 9-62. 



I hope before long to be able to lay before the Society the results of 

 specific gravity determinations of the vapours of other compound and 

 elementary bodies, together with the whole of the experimental details. 



VIII. " Extract from Report to Professor Sir Wyville Thomson, 

 F.R.S., Director of the Civilian Scientific Staff, on the 

 Brachiopoda dredged by H.M.S. ' Challenger.' " By Thomas 

 Davidson, F.R.S. Received May 8, 1878. 



At the request of Professor Sir Wyville Thomson, I have under- 

 taken the examination, description, and illustration of the Brachiopoda 

 dredged by the ' Challenger ' Expedition. 



Very little seems to have been known with respect to recent Brachi- 



