34 



HARD WICKE ' S S CIENCE- G O SSI P. 



of gas first explodes and raises a cloud of inflammable 

 particles. These, heated by the flame of the gas, 

 combine with the oxygen of the air suddenly and 

 explosively, as in flour-mill explosions ; more dust is 

 thereby raised and exploded, and thus it travels like 

 firing a train of gunpowder. 



The Prevention of Dangerous Colliery 

 Explosions. — The above suggest very obvious 

 practical lessons. Every colliery should be kept 

 free from considerable accumulations of dust. In 

 ordinary collieries, where there is much water, this 

 may easily be done by a hose. In the collieries of 

 the future, where we shall be working the deeper 

 coal at depths only limited by the heat, the pits 

 will be dry, and, as I have already explained (see 

 "Limits of Coal Supply," in my " Science in Short 

 Chapters "), surface water and intermediate springs 

 will then be largely used for cooling purposes. These 

 hot and dry workings will be especially exposed to 

 terrible results from dust explosions, and therefore 

 the necessity for a clear understanding and practical 

 recognition of this source of clanger becomes con- 

 tinually more and more urgent. Once understood, 

 and thus recognised, prevention of serious calamities 

 is easy enough. 



My first underground experience was in descending 

 a small trial shaft, and following a trial drift, under 

 the guidance of a "larkish" young colliery engineer. 

 When we arrived at the end of the drift he recognised 

 a small blower, took a match from his pocket, 

 and lighted it. A small but rather startling flash 

 resulted, followed by a most alarming sense of 

 suffocation. When above ground I remonstrated, 

 and received reply that my conductor knew by the 

 state of his lamp that there was no dangerous 

 quantity of fire-damp, and therefore a good oppor- 

 tunity of giving me a taste was afforded. This 

 "baptism of fire," though unpleasant, was very 

 instructive, as it proved that an experienced collier 

 can, by means of his lamp, form some estimate of the 

 extent of danger ; and, with the additional light 

 thrown on the subject by Mr. Galloway's experiments, 

 explains the fact, that explosions have in so many 

 cases extended to roads and workings where no sane 

 collier would have remained had it been charged 

 with sufficient gas to be dangerous alone. If there is 

 enough hydro-carbon gas to form with the air an 

 explosive mixture, there is enough to fill the cage 

 of the Davy lamp with the warning flame that is too 

 terrible to be unheeded. The collier who would at 

 once retreat and raise alarm on seeing this, now 

 passes without heed any amount of accumulated 

 coal-dust on pillars, walls, roofs, and dry floor of the 

 pit, because he is ignorant of its dormant yet fatal 

 energies. 



Porpoise Milk.— Mr. Purdie has published in 

 the " Chemical News" an analysis of porpoise milk, 



which is very curious. To show its peculiarity, I 

 state below the composition of the milk of some 

 other animals, for comparison with that of the 

 porpoise : — 



Woman 



Cow 

 Goat 

 Ass. . 

 Sheep . 

 Uitch . 



Water. 



88-6 

 87-4 

 82-0 



9°'5 



85-6 

 66 '3 



Fat. 



2-6 

 4-0 

 4'5 

 i"4 

 4"5 

 14-8 



Sugar and 1 Ni f°genous 



soluble salts. F om P° u . nd *«* 

 : insoluble salts. 



4*9 

 5"o 



4"5 

 6-4 



4"a 



2-9 



3 

 3' 

 9' 

 1' 



5' 

 16' 



The porpoise milk examined by Mr. Purdie was- 

 yellow, thick, and had a fishy odour, and was com- 

 posed of water 41 - i 1 ; fat 45*80 ; albuminoids 1 1-19 ^ 

 sugar 1-33 ; and ash 0-57 per cent. 



The curious difference is the very large propor- 

 tion of fat : more than eleven times as much as in 

 cow's milk, or nearly eighteen times as much as in 

 woman's milk. It is probably connected with the 

 demand for blubber by the young porpoise ; and, if 

 so, does not support the conclusions of those physio- 

 logists who have lately denied that the fat of food 

 does not form the fat of the animal that eats it. It 

 would be very interesting to compare the composition 

 of the milk of an Esquimaux woman with that of a 

 negress — the Arctic with the tropical variety of the 

 same species. 



Digestibility of Cheese.— Klenze has experi- 

 mented on eighteen kinds of cheese, and finds that 

 Cheddar was digested in the shortest time (four 

 hours). Unripe Swiss cheese required ten hours. 

 He concludes that fat cheeses are dissolved more 

 readily than hard skim-milk cheeses, because the 

 fat renders them more open. He finds no connec- 

 tion between the digestibility and the percentage of 

 water in the cheese, but that ripeness is favourable. 



Manuring Vines with Copper. — Many investi- 

 gations have lately been made upon the absorption 

 of soluble metallic salts by the rootlets of various 

 plants, and the distribution of the metal in the plant. 

 The vine has thus been manured with sulphate of 

 copper, mixed with lime, by MM. Millardet and. 

 Gayou. They find that most of the copper is de- 

 posited in the leaf — that merely a doubtful trace can 

 be found in the juice of the grape. Other experi- 

 ments with other salts and other plants indicate thai 

 the chlorophyll of the leaves is the most addicted 

 to picking up the foreign matter. Tea-leaves, for 

 example, contain much iron, doubtless due to the 

 ochreous soil on which they best grow. The 

 analytical myth concerning the adulteration of tea 

 with iron filings is thus explained. When roasted, 

 the iron salt in the leaves is reduced to magnetic 

 oxide, and the leaves are therefore attracted by a 

 magnet. 



