612 REPORT — 1894. 



the coals in one ' field ' are found under different physical and chemical conditions 

 from those of another, and little evidence is obtained by comparison. 



The decomposition of peat and of wood teaches us more of the chemistry 

 of coal formation. In both instances the woody fibre disappears first, leaving a 

 residue richer in resinoids. The lignites of Bovey Tracey have, as in the case of 

 decaying peat and wood, an excess of resinoid matters over the vegetation which 

 formed them. Hutton found mineral resin in Carboniferous coals, and others since. 

 Witham showed long ago, and much recent evidence proves, that conifers and 

 other dicotyledons flourished during the Carboniferous period. Just as lime and 

 other trees shed saccharine matter on the leaves and grass underneath, so it is 

 probable that liquid, gummy, and resinous matters were showered from the forest 

 vegetation during the Carboniferous and Tertiary periods. 



The chemical changes in coal formation took place chiefly at and near the 

 surface. In the formation of paraffin shale and some Scotch cannels the woody 

 fibre of the forest growths was destroyed, little else but bituminous matters remain- 

 ing. A resinous vegetation without much dicotyledonous trees, or if with dicotyle- 

 dons, considerable surface exposure and decomposition of the woody fibre, would 

 produce rich bituminous coal, Wigan cannel, &c. A. luxuriant resinous and 

 dicotyledonous vegetation, assisted by heat and pressure, without much surface 

 decomposition, probably gave rise to semi-bituminous, steam, and anthracite coal. 



Our present chemical knowledge of coal may be summed up as follows:— 



1. It contains water after air-drying. The hygroscopicity of coal has not 

 received due attention. The water "is in chemical combination. Further, the 

 hygroscopicity is most probably the key to the spontaneous combustion of coal. 



2. Coal contains the gases,"liquid?, and solids of the parafiin series, but these 

 tot'ether will not make up more than 1 per cent, of Carboniferous coals. 



"3. The bulk of coal is carbon, with more or less hydrogen, oxygen, nitrogen, 

 sulphur, and ash. We shall probably never know how the carbon is combined or 

 bow much is in the free state. 



Further experiments are suggested as follows : — 



1. Upon the decomposition of dicotyledons to throw light upon the formation 

 of coal. 



2. Upon the hygroscopicity of coal ; and to study its bearings upon the 

 spontaneous combustion of coal on board ship. 



3. Upon coals from all Briti.sh coal-fields, to determine the quantity and, if 

 possible, the constituents soluble in gasolene (petroleum ether) or benzine a» 

 employed by Mr. Watson Smith. 



4. To act upon the various coals with a weak solution of potassic hydrate. 



6. On the Iodine Value of Sunlight in the High Alps. By Dr. S. Rideal: 



At the meeting of the A^ociation in Nottingham I had an opportunity of sub- 

 mitting the values of the sunlight in the Upper Engadine in terms of the amount 

 of iodine liberated from an acidulated solution of potassium iodide during th© 

 month of January 1893. These experiments have been continued during the 

 months of January and February of the present year by my brother, A. W. Rideal, 

 and the results may therefore not be without interest. The recent experiments 

 were conducted in exactly the same way as those of last year, so that in all respects 

 they are strictly comparable. 



The solutions were standardised by standard iodine solution prepared in 

 England, and the hvposulphite solution was checked against this solution from 

 time to time during the progress of the experiments. 



During the last winter the weather was, on the whole, bad, and the number of 

 days on which snow fell or which were overcast were more numerous than in the 

 corresponding period of last year. 



The maximum value was obtained on February 4, and was equal to 1452 mgms. 

 of iodine per 100 c.c, as compared with 13-5, the maximum value on January 1, 

 1893. The lowest value was 3-53 on December 9, 1893, as against 5*7 on 



