110 



CHEMISTRY. 



ually causes a rise in temperature. If the coal 

 is finely powdered, the absorbing and heating 

 powers become very important, while the rate of 

 action increases as the temperature rises, but is 

 rarely sufficient to bring about spontaneous igni- 

 1 ion." When the carbon of the coal absorbs oxy- 

 gen the compressed gas. becomes very active 

 chemically and soon begins to combine with the 

 carbon and hydrogen of the bituminous portions 

 of the coal ; the chemical activity increases with 

 the temperature, and is accompanied by a further 

 increase of heat. The effects work cumulatively 

 upon one another, and if the access of air is free 

 enough, the temperature reaches the igniting 

 point of the coal. The result is hastened by the 

 presence of pyrites in the coal, which is also 

 acted upon chemically by oxygen ; but pyrites 

 is not itself capable of causing combustion. The 

 liability to spontaneous ignition of coal in ships 

 increases with the increase of tonnage in cargoes ; 

 with the length of the voyage, particularly if 

 it is prosecuted into warm regions; and is 

 affected by the kind of coal, some coals being 

 more liable than others, to spontaneous heating 

 and ignition ; by the fineness of the division of 

 the coal ; by wetting combined with richness in 

 pyrites; by the ventilation of the cargo; and 

 by heat from the furnaces and boilers. The 

 author's paper concludes with a summary of the 

 precautions that may be taken against the heat- 

 ing of coal in cargo. 



Previous to the formation of the clasification 

 of the elements with which the names of New- 

 lands and Mendeleeff are associated, numerical 

 relations between the atomic weights of allied 

 elements were discovered by Dobereiner, Dumas, 

 and other chemists. It is now shown by Mr. P. 

 J. Hartog, in " Nature," that M. A. E. Beguyer de 

 Chancourtois, a French geologist, was the first 

 to publish a list of all the known elements in the 

 order of their atomic weights. In a communi- 

 cation to the French Academy in April, 1862, he 

 described " a natural classification of the simple 

 bodies and radicles by a table in the form of a 

 helix, founded on the use of numbers, which I 

 call characteristic numbers or numerical charac- 

 teristics." These numbers were deduced from 

 the measurement of the chemical equivalents of 

 the bodies; when arranged on his helical table, 

 or on a plane surface representing it, they gave 

 what he called characteristic points or geomet- 

 rical characters. He then anounced as the fun- 

 damental theorem of his system that " the re- 

 lations between the properties of different bodies 

 are manifested by simple geometrical relations 

 between the positions of their characteristic 

 points " ; and that likenesses and differences are 

 manifested by a certain numerical order in the 

 succession of bodies, " for example, immediate 

 sequence or alternation at various periods." The 

 subject was further pursued in a memoir com- 

 municated in March, 1803. The papers have not 

 been printed in full. Newlands's first paper on 

 the numerical differences between the atomic 

 weights of allied elements was published in Feb- 

 ruary, 1863; and his second, in which he ar- 

 ranged the elements in the order of their atomic 

 wight.s, in July, 1864. 



Baking powders consist essentially of a car- 

 bonate or bicarbonate to supply carbonic-acid 

 gas, and an acid which can liberate it, with some 



inert substance, usually starch, to temper the 

 chemical action. They may be classified as fol- 

 low according to their acid constituents, with 

 which bicarbonate .of soda is usually associated : 

 Tartrate powders, in which tartaric acid is the 

 acid constituent, and which leave the least ob- 

 jectionable residue ; phosphate powders, in which 

 mono-calcium phosphate furnishes the acid, and 

 with which the residues, though larger in quan- 

 tity, are not otherwise more objectionable than 

 those of the tartrate powders; and alum pow- 

 ders, in which the gas is set free by the action 

 of either potassium or ammonium alum. The 

 effect of the residues from these on the human 

 system has not been determined. In general, it 

 may be said of the three classes of powders, that 

 a tartrate powder gives the lowest percentage 

 of carbon dioxide in proportion to the weight 

 of chemicals used, together with the least weight 

 of residue; and a straight alum powder gives 

 the highest proportion of gas and greatest weight 

 of residue. The report of the chemical division 

 of the Agricultural Department suggests that 

 with a little care baking powders could be made 

 at home at much less cost than the market 

 price. 



The results of the many determinations that 

 have been made of the alkaloid in teas are re- 

 garded by David Hooper, of Ootacamund, India, 

 as showing that no relation exists between the 

 amount present and the commercial value of 

 the leaf. The tannin of tea has also been in- 

 vestigated, but as the subject has been treated 

 by so many experts, using different methods and 

 applying them to different samples, the results 

 are not comparable, and leave the matter open 

 for further inquiry. From analyses of sixty-five 

 specimens of Indian and Ceylon teas. Mr. Hooper 

 finds that the finest teas are those which contain 

 the most tannin, and that the elevation does not 

 appear to affect the amount of tannin, as has been 

 supposed. The determinations of two of the speci- 

 mens indicate that the kind of shrub cultivated in 

 India contains more or less tannin according to its 

 original habitat. The amounts of tannin shown 

 in Mr. Hooper's list are obtained by perfectly 

 exhausting the leaves, and do not represent the 

 amount taken in domestic use. The infusion of 

 the family tea-pot extracts more or less tannin, 

 according to the sample used and the time al- 

 lowed for the leaves to soak in boiling water. 

 The broker's test of five minutes takes out one 

 fifth of the extract, with a corresponding amount 

 of tannin. The tea-pot infusion of ten minutes 

 removes about one third, fifteen minutes one 

 half, and twenty minutes two thirds. The tannin 

 is the source of the " strength " of the tea, and 

 the higher the tannin the richer the infusion, 

 and the more of body will the sample possess. 

 Tannin is likewise a natural constituent of the 

 tea, and is not amenable to suppression by high- 

 er cultivation, or by the ordinary processes of 

 manufacture. 



The results of an examination of the cuticular 

 constituents of flax fiber have been published by 

 C. F. Cross and E. J. Bevan. On exhaustion 

 with boiling alcohol, the fiber lost from 3 to 4 

 per cent, of its weight ; in cooling the solution 

 deposited a greenish-white resin, which yielded, 

 on hydrolyses with alcoholic soda, a wax alco- 

 hol, identified as ceryl-alcohol, and a ketone-like 



