HARDWICKE'S SCIENCE-GOSSIP. 



75 



that in most cases the quantity of a given substance is 

 determined by dissolving the mixture in which it is 

 contained, and then adding a precipitant, which 

 throws down the substance in question in solid 

 insoluble form, usually a compound of known 

 composition. The solid is separated by filtration and 

 weighed. The filtering agent must be removable, 

 and blotting paper answers the purpose admirably. 

 If the precipitate is incombustible, the paper is 

 burned with its adhering precipitate, which is then 

 weighed. Otherwise, it is weighed on the paper, 

 after drying ; another piece of paper of equal size and 

 proved equal weight, being used as counterpoise. 

 Specially made paper that leaves but an infinitesimal 

 ash is used. 



In the Records of the Geological Survey of India, 

 vol. 1 7, is a memoir by Dr. \V. King, on the " Smooth 

 Water Anchorages of Narrakal and Alleppy," on the 

 Travancore Coast. These remain smooth even when 

 the surface of the sea outside is torn by the south- 

 westerly moonsoons into white surf-topped billows. 

 The explanation of the mystery is simple enough, and 

 is interesting, as affording further evidence on the 

 disputed question of oiling the waves. The bottom 

 of these anchorages is a soft, unctuous mud found to 

 contain oil, and from it is a continuous oozing 

 upwards of petroleum. My friend Arthur Robottom 

 describes a similar calm region on the Californian 

 coast, but at some distance out at sea. Here the oil 

 wells up in large quantities, spreads visibly over the 

 surface and effectively becalms a great area around 

 the spring. Franklin's experiments on the ponds of 

 Clapham Common, and his conclusion, that the oil 

 prevents the wind from taking hold of the water, by 

 acting as a lubricant against the wind-friction, are 

 confirmed by these cases, by the experiments at 

 Peterhead, and by all that has since been learned on 

 the subject. 



In the same volume is an account of a fiery 

 eruption from one of the mud volcanoes on Cheduba 

 Island, where a body of flame 600 feet in circumfer- 

 ence is said to have at one time reached an elevation 

 of 2400 feet. Petroleum again. The earth evidently 

 contains a much larger store of petroleum than is 

 usually supposed. 



Very few people appreciate the interesting collection 

 of meteorites in the British Museum. The majority 

 of ordinary visitors pass through the whole of the 

 show without seeing them at all. A very interesting 

 addition is about to be made to this collection — will 

 pdssibly be there when this is printed. It is a 

 meteorite, weighing 46 kilos (101J lbs.), which was 

 discovered in the autumn of 1882, near Durango, in 

 Mexico, at a depth of about a foot. The slight depth 

 and other indications have led to the inference that it 

 had fallen quite recently. Its composition is : iron, 

 91*78; nickel, 8*35; cobalt, o*oi ; with traces of 

 phosphorus and carbon. Specific gravity, 7 '74-7 '89. 

 The detection of the ordinary adulteration of milk 



by water is unsatisfactory, on account of the varying 

 composition of the milk from different cows, and 

 even from the same cow at different periods. The 

 milk of an Alderney or Jersey cow may be much 

 diluted, and yet, when tested by the proportion of 

 water to cream, shall come out richer than the milk 

 from some other cows when unmixed. The method 

 recently introduced by M. Sambuc is said to over- 

 come this difficulty. Experiments made by him in 

 1879, an d m October and November of last year, 

 show that the serum of the milk — that which is left 

 when the casein and cream are removed, varies very 

 little in specific gravity, never falling below i , 0278. 

 To effect its separation, the milk is heated to 40 - 

 50 C. (104 to 122 F.), and an alcoholic solution of 

 tartaric acid is added. After about a quarter of an 

 hour the mixture is taken from the fire, agitated with 

 a small bundle of twigs, and strained through a linen 

 filter. The specific gravity of the serum or whey is 

 then determined by a lactometer. 



In Dingler's " Polytechnisches Journal," vol. 254, 

 p. 443, is an account of a method of enamelling casks 

 invented by F. G. Sponnagel, and apparently not 

 patented. Instead of coating the wood with enamel, 

 the cask or vat is first treated with an aqueous solution 

 formed by fusing 100 parts of silica with 50 parts of 

 alkali, and when this has penetrated the wood 

 thoroughly the cask is filled with a solution of alumi- 

 nium acetate in water mixed with sulphurous acid in 

 the proportion of 4 : 2 : 1. , This effects a precipitation 

 of neutral enamel of silicate of alumina within the 

 pores of the wood. Assuming that such precipitation 

 is successfully effected, we obtain in such internally 

 enamelled wood a material of great usefulness for a 

 multitude of purposes besides cask making. 



In the same volume of the same Journal, page 399, 

 an honest method of manufacturing soap is described. 

 Perhaps I should explain what I mean by honesty as 

 applied in the manufacture of soap. Shrewd, 

 observant house-wives know that bars of soap when 

 stored in a dry place have a curious habit of shrinking, 

 and that the amount of shrinkage varies with the 

 samples. Not very long ago a petty fraud was rather 

 extensively perpetrated by a gang of vagabonds, who 

 strolled from door to door in poor neighbourhoods* 

 offering '" salvage soap " for sale. They told a tale of 

 the shipwreck of a cargo of soap, and how it was 

 damaged by sea water, how they had bought it cheap 

 and could sell at three-halfpence or twopence per 

 pound. The soap was sufficiently wet to correspond 

 with the story. It contained 70 or So per cent, of 

 water, on the evaporation of which a long bar 

 shrivelled to a short twisted stick. Ordinary soap of 

 fair quality contains 20 to 25 per cent, of water, but 

 may be made to contain much more, even the salvage 

 quantity. Pure soap is a compound of fatty acids 

 with alkali, no free alkali remaining. Such remaining 

 alkali renders it irritant to the skin, though suitable 

 enough for washing greasy clothes or very dirty 



E 2 



