146 



CHEMISTRY. 



frequently possessing a pink tint. The chemi- 

 cal analysis of the crystals led to the for- 

 mula HCaAsO + 2H.jO ; and the substance 

 thus becomes chemically as well as physically 

 isomorphous with brushite, the corresponding 

 phosphate of calcium, HCaPO 4 + 2H a O. 



Atomic Weights. The following new method 

 for the determination of the atomic weight 

 of oxygen was described by "W. A. Noyes at 

 the American Association : 



The apparatus to be used consists of a U-tube, filled 

 with copper oxides, to one side of which is attached a 

 tube with a capacity of about 20 cc., and to the other 

 side a three-way stop -cock. The U-tube is first ex- 

 hausted and weighed ; it is then heated, and pure 

 hydrogen is passed in. The hydrogen is converted 

 into water, which then condenses in the tube on the 

 opposite side from the stop-cock. The gain in weight 

 of the apparatus gives the weight of the hydrogen. 

 After weighing, the gases remaining in the apparatus 

 are pumped out and analyzed. The water is also ex- 

 pelled, and from the loss in weight of the apparatus 

 the weight of oxygen is determined. The advantages 

 of the method are : The weight of the hydrogen is 

 determined directly ; the weight of the oxygen is also 

 found directly and independently of the weight of the 

 hydrogen ; each is weighed in a vacuum, and the 

 usual correction of the weights to a vacuum becomes 

 unnecessary ; impurities in the hydrogen, and espe- 

 cially any nitrogen which it contains, will be detected 

 and the amount determined ; finally, no error can re- 

 sult from incomplete combustion of the hydrogen. 



In the report of the Committee on Electrol- 

 ysis of the British Association, a direct de- 

 termination of the ratio between the atomic 

 weight of copper and that of silver, based upon 

 the electrolytic experiments of W. N. Shaw, is 

 madeto give Ag:Cu 17:10; whence the atomic 

 weight of copper is made 63-333, or, corrected, 

 63-360. This value being different from that 

 ordinarily received, a direct determination was 

 made, at the request of Prof. J. P. Cooke, by 

 T. W. Richards. This experimenter deduced 

 an atomic weight for copper of 63 - 44, which, 

 although it does not exactly coincide with 

 Shaw's results, is nearer to them than the old 

 accepted value of 63-17. 



The atomic weight of didymium, freed from 

 all other, allied metal:; known at that time, was 

 determined by Cleve, in 1874, as 147. After the 

 discovery of samarium as an accompaniment 

 to didymium, and under evidence that it was 

 present in the sample examined by him, the 

 author made a new determination of the atom- 

 ic weight of didymium, freed from samarium, 

 as 142-3. 



"With the atomic weight 198*6, osmium has 

 formed a notable exception to the periodic 

 law, standing at the opposite end of the plati- 

 num group from where its other properties 

 would place it. The atomic weight of this 

 metal has now been redetermined by Prof. 

 Seubert by means of the analysis of the pure 

 double chlorides of osmium with ammonium 

 and potassium, and is fixed at 191-1. This gives 

 to it its proper place in the periodic classifica- 

 tion, as before indium. 



Considering that it is desirable that all deter- 

 minations of atomic weights should be con- 



nected as directly as possible with hydrogen, J. 

 W. Mallet describes a method by which this may 

 be done in the case of gold. A known weight 

 of zinc is dissolved in dilute sulphuric acid, and 

 the hydrogen evolved is measured. A solu- 

 tion of bromide or chloride of gold is then 

 treated with zinc more than sufficient to pre- 

 cipitate the whole of the gold, the residual zinc 

 being determined by the hydrogen evolved on 

 treatment with sulphuric acid. The difference 

 in volume of hydrogen obtained gives a direct 

 means of calculating the atomic weight of gold. 



Chemistry of Plants. Helen C. De S. Abbott 

 is convinced that a similarity of one or more 

 chemical constituents is to be found in all 

 plants which have reached the same stage of 

 evolution that there is a development in 

 chemical constitution, closely connected with 

 their morphological evolution, which plants 

 pass through and hence that chemical char- 

 acter, as indicating the height of the plant in 

 the scale of progression, is essentially appro- 

 priate for a basis of classification. Some one 

 compound, as saponin, will be found with simi- 

 lar botanical characters in plants of distinct 

 genera and families on the same plane of evo- 

 lution or development. Chemical constituents 

 of plants are found in varying quantities dur- 

 ing stated periods of the year. Certain com- 

 pounds present at one stage of growth are ab- 

 sent at another. Different parts of plants may 

 contain distinct compounds ; whether any of 

 the constituents found in plants are, as has 

 been said, the result of destructive metabolism, 

 and of no further use in its economy, or not, 

 it is a significant fact that certain cells, tissues, 

 or organs peculiar to a plant secrete or excrete 

 compounds peculiar to them which are to be 

 found in one family, or in species which are 

 closely allied. 



The chemistry of the onion as a field-crop 

 has been studied by R. W. E. Mclvor, in Aus- 

 tralia. The soil in which the plant is grown 

 is a chocolate loam of basaltic origin contain- 

 ing in a virgin state sometimes as much as 0-28 

 per cent, of nitrogen and 0-20 per cent, of phos- 

 phoric acid extractable by hydrochloric acid. 

 "While non-nitrogenous guanos and superphos- 

 phates have in a few instances slightly increased 

 the crop, it has been found that manures con- 

 taining , nitrogen in the form of sulphate of 

 ammonia or as a constituent of blood-guano 

 produce more satisfactory results. The liberal 

 use of superphosphate mixed with sulphate of 

 ammonia has invariably proved more beneficial 

 on the poorer land than superphosphate alone. 

 The largest returns, however, have resulted 

 from the joint use of a fertilizer composed of 

 the sulphates of ammonia and potash and su- 

 perphosphate. The farmers are of opinion that 

 onions produced by the aid of purely chemical 

 manures keep in good condition for a longer 

 period than those obtained from ground which 

 is naturally " forcing," or which has been re- 

 cently manured with rich farmyard manure. 

 It seems fairly clear to the author that the on- 



