464 



NATURE 



{Sept. 23, 1875 



ing : — The water of the river, after being mechanically strained 

 from solid impurities, is passed into tanks, where it is mixed with 

 sulphate of alumina ; it is then passed to a second set of tanks where 

 it is mixed with milk of lime, and thence on to a field or filter 

 bed i,\ acres in extent, which ejects 80,000 gallons of water per 

 hour, pure enough for fish to live in. The greatest difficulty to 

 be contended with was the freeing of the precipitated matter 

 from the water, of which it contained 80 per cent. ; this quantity, 

 however, was considerably reduced by means of mechanical 

 appliances, which reduced the water to such a percentage that it 

 could either be dried (and so rendered portable) by |heat, or by 

 mixing it with some substance which increased its manurial value. 

 In conclusion, the author stated that the primary object was to 

 secure sanitary rather than commercial success, and that this cer- 

 tainly had been achieved at a cost of about sixpence per head per 

 annum for a population of 40,000. — Some discussion ensued as 

 to the relative merits of the method of irrigation and the method 

 just described. — In reply, Mr, Melliss said that he was not pre- 

 pared to say that the Coventry method was the best in all 

 localities ; the physical characteristics of the land in neighbour- 

 hood must always be taken into account, as of course it would 

 make a great difference whether the soil consisted of clay or of 

 sand. 



Prof. Debus read a paper On the chemical theory oj Gunpowder, 

 in which he stated that nothing illustrated in so striking a manner 

 the molecular changes produced by chemical aclion as the ex- 

 plosion of gunpowder. He said that some years ago the 

 eminent French chemist Berthelot showed that if COg be passed 

 into a mixture of BaO and CaO in insufficient quantity to preci- 

 pitate the whole of the barium and calcium as carbonate, then 

 neither is the whole of the barium precipitated nor the whole 

 of the calcium, but they are precipitated in a certain definite 

 proportion, which is a multiple of their molecular weights. 

 Hence, in general, if a mixture of the salts A and B be decom- 

 posed by some other substance, C, in insufficient quantity to 

 decompose the whole of both, then the bodies formed will be 

 ACj + BC2 where Cj + Cg = C ; and moreover, if the quantity 

 of B is doubled or trel)led, &c., the quantity Cg will be increased 

 in a definite proportion. After makmg some further remarks of 

 a like nature on the decomposition of a mixture of BaClj and 

 CaClg by CO2, and also of the explosion of mixture of H and CO 

 with an insufficient supply of oxygen (as investigated by Bunsen), 

 the Professor went on to show that the same arguments might 

 be appUed to the explosion of gunpowder which was a mixture 

 of carbon, sulphur, and nitrate of potash. 



He then placed upon the. black board the result of one of a 

 large number of analyses of one grain of powder. 



Compound. Grain. 



(1) K2CO3 -3098 -00224 



(2) K2S2O3 -0338 -000177 



(3) K2SO4 -0658 -000378 



(4) KgS -1055 -00096 



(5) CO -0473 -00170 



(6) CO2 -2770 -0629* 



In addition to these were also formed in small quantities the 

 following : potassium sulphocyanide, potassium nitrate, am- 

 monium carbonate, sulphur, sulphuretted hydrogen, marsh gas, 

 hydrogen, and nitrogen, most ot which appear to have been the 

 result of gaseous impurities in the carbon. 



Referring to the table it will be seen that by adding up the 

 total molecular value of the sulphur salts we gee -00151, which 

 bears to the molecular weight of potassium carbonate ('00224) 

 the ratio 2 : 3 nearly. Plence it is inferred that at the first 

 moment of combustion the potassium in the saltpetre divides 

 itself into five parts, two of which go to unite with the sulphur, 

 and three to', form the carbonate. Again, it will be seen that the 

 carbonic oxide bears to the potassium very nearly the simple 

 ratio 3 : 4. The CO2 must have been formed in more than one 

 reaction, because it does not give any simple molecular ratio. 

 The conclusions thus arrived at are, that in the first moment of 

 explosion the sulphur existed either as sulphite or as sulphate, 

 and that the .carbonic oxide must have been formed simul- 

 taneously with the potassium carbonate. The equations of the 

 decomposition of gunpowder would then be the following : — 



(1) 24KN03 + C35 + 0=I2K2C03 + 9C03+I4C02+I2N2 



(2) I6KN03 + C8 + S8 = 8K2SO,-^8C02 + 8N2 



(3) 6K2S04 + Cll-^S-^0 = 5K2S + K2S203 + IIC02. 

 The first two reactions taking place simultaneously. 



* The third column is the number found by dividing each quantity by the 

 corresponding molecular weight. 



Prof. Thorpe, in giving some account of a New Compound of 

 Fluorine and Phosphorus, said that having had some occasion 

 recently to make a considerable quantity of the terfluoride of 

 arsenic, by heating calcium fluoride with arsenious acid in the 

 presence of Nordhausen sulphuric acid, he was induced to study 

 the behaviour of this body with various other substances. When 

 this terfluoride of arsenic is dropped into a solution of the penta- 

 chloride of phosphorus, such an immense amount of heat is evolved 

 that it is necessary to keep the vessel surrounded with a freezing 

 mixture, and dense white fumes are given off, while only chloride 

 of arsenic remains in the solution. This gas is decomposed by 

 water, but may easily be collected over dry mercury, in which 

 condition it may be kept, but after some time the glass is observed 

 to become dim. The specific gravity of the gas answers to the 

 formula PF5, and its molecular weight is 63. It acts readily 

 upon alcohol, but the substance formed quickly corrodes glass. 

 It is believed that it will be found to be a condensable gas under 

 a pressure of six or seven atmospheres. It is not impossible that 

 when decomposed by the electric spark it may ^wt fluorine. It 

 is remarkable as the only known pcntatomic compound of phos- 

 phorus. 



Mr. B.J. Fairley, F.R.S.E., read a paper On New Solvents 

 for Gold, Silver, Plati^ium, ^'c, with explanation of so-called 

 Catalytic Action of these Metals and their Salts on Hydrogen 

 Dioxide, in which he stated that it was perfectly easy to dissolve 

 silver in dilute acids, as acetic, sulphuric, or hydrochloric, pro- 

 vided hydrogen dioxide were present in the solution, and that if 

 under the same circumstances the silver were dissolved in nitric 

 acid no lower oxides were evolved. Repeating the experiments 

 with gold, it was found that acetic and nitric acids scarcely dis- 

 solved it at all, but hydrochloric acid readily, and without the 

 evolution of free chlorine. Some remarks were also made on 

 the great liberation of heat observed when two unstable com- 

 pounds of oxygen react upon one another so as to produce more 

 stable compounds, especially with reference to the heat evolved 

 during the decomposition of ozone and hydrogen dioxide, the 

 author stating that this great heat must correspond to a great 

 force of union. 



The same gentleman also made some remarks On the Use of 

 Potassium Dichromate in Groves and Punsen's Batteries to 

 ensure constancy, in which he stated that he had used a small 

 quantity of that substance dissolved in the nitric acid, and had 

 found that the battery remained constant so long as any chromic 

 acid remained to be reduced, and that no red fumes appeared. 



Two other papers were also communicated by the same author : 

 (i) On a Nr^v Process for the separation of Lead, Silver, and 

 Mercury {Mercurous) Salts ; (2) On a Process for the Preparation 

 of Periodates, with their application as a Test for Iodine and 

 Sodium. 



Dr. J. H. Gladstone read a paper On the relation of the 

 Acids and Bases in a mixture of Salts to the original manner of 

 combination. In a former set of experiments the author had 

 shown that if a molecule of copper nitrate and a molecule of 

 potassium sulphate be dissolved in any quantity of water, and 

 two molecules of potassium nitrate with one molecule of copper 

 sulphate be dissolved in an equal quantity of water, then the 

 colour produced is the same : and similarly for other sets of salts. 

 The author, however, thought that the colours of these mixtures 

 being comparatively faint, it would be better to try mixtures 

 of colourless salts, and add to these mixtures some substance 

 such as ferric sulpho-cyanide, ferric mreconate, or bromide 

 of gold, whose colour is easily reduced. Accordingly, he mixed 

 together potassium sulphate and magnesium nitrate, and the 

 corresponding salts potassium nitrate and magnesium sulphate ; 

 also acetate of potassium and nitrate of lead, and the correspond- 

 ing salts, &c. ; in every case these were found to reduce the 

 colour of ferric sulpho-cyanide equally. All the experiments 

 united to confirm the supposition that the effect of a mixture 

 does not depend upon the position of the acids and bases in it, so 

 long as the proportions of each remain the same. 



Dr. Russell asked if the amount of colour would indicate a 

 small change in the nitrate, and also if the element time had been 

 taken into the experiments. 



Dr. Tilden preferred the old method, on the ground that by 

 adding a reagent new conditions are introduced. 



In reply. Dr. Gladstone said that the ferric sulpho-cyanide 

 was much more delicate than the solutions of copper salts. 



Dr. J. H. Gladstone read two notes, On the Copper-Zinc 

 Couple, by himself and Mr. Alfred Tribe. In the first he showed 

 that whereas a piece of zinc in dilute sulphuric acid (3^ in 1,000 

 parts of water) gave off seven volumes of hydrogen in one hour, 



