October 28, 1909J 



NA TURE 



521 



phorus, and was therefore enabled to calculate their 

 respective atomic weights by the physical method. 

 For mercury the ratios are Hg/O, (physical) and 

 Hg/O (chemical), and for phosphorus V JO., (physical) 

 and P/O (chemical). 



These discrepancies forced Berzelius to limit the 

 " volume-theory " to gaseous elements, and to such as 

 are easily converted into gas. F"inally, when dis- 

 crepancies, no less serious, arose in the case of sulphur 

 and of arsenic, he decided to abandon the theory 

 This was in 1833, after he had held to it for twenty 

 years. 



The only sound application of the law to theoretical 

 chemistry was made by Avjgadro in iSii. In con- 

 sidering his teaching, it is best to set aside the word 

 atom and its associations, at least in the first place, 

 .and to use the word " molecule " instead. Avogadro's 

 hypothesis is that equal volumes of different gases 

 contain the same number of molecules. In that case 

 the weights of equal volumes of gases are proportional 

 to their molecular weights. 



The hypothesis has a special fnd important conse- 

 quence regarding the constitution of the molecule. 

 For instance, each molecule of hydrogen, with the 

 necessary chlorine, yields two molecules of hydro- 

 chloric acid. But each molecule of the acid contains 

 hydrogen, and therefore the hydrogen molecule has 

 certainly been halved. This conception of the molecule 

 of an element as a thing which may consist of parts 

 is an inevitable consequence of Avogadro's hvpothesis, 

 and it was boldly accepted by him. The mere possi- 

 bility of such a thing was scouted by Thomson, and 

 Berzelius, and Graham as utterly subversive of the 

 atomic theory. Yet it forced itself forward again and 

 again upon Ampere, Dumas, Prout, VVaterston, 

 Kronig, Gerhardt, Laurent, Clausius. Finally, in 

 i860, Cannizzaro was able to convert chemists to 

 Avogadro's hypothesis and all its consequences. Since 

 then the hypothesis, based as it is upon Gay-Lussac's 

 law, has been the fundamental doctrine of chemistrv. 



One thing about the definition of the law is worth 

 noting. Nothing is said in it, but much is implied, 

 regarding the conditions under which the gases are 

 measured. The teacher would do well to direct atten- 

 tion to this. There is the obvious assumption that 

 the different gases concerned in a particular experi- 

 ment are measured under the same temperature and 

 pressure But the definition implies another assump- 

 tion, namely, that different gases behave in the same 

 way under the same conditions. Otherwise the com- 

 bining ratio, say, of hydrogen and chlorine, could not 

 remain constant over a range of temperature and 

 pi cssure. 



Of course, we know that the combining ratio of 

 two gases does not remain strictly constant when the 

 conditions alter. The fact that a gas such as carbon 

 dioxide deviates considerably from Boyle's law and 

 Charles's law leads to the expectation that Gay- 

 Lussac's law is itself only an imperfect description of 

 the facts. The expectation is verified, for even the 

 combining ratio of hydrogen and oxygen is not 

 strictly 2 : i, but has been ascertained to be 2'oo2S5 

 (Scott), 2'0037 (Leduc), and 2^0027 (Morley). This is 

 an important consideration, for molecular and atomic 

 weight data obtained on the assumption that Gay- 

 Lussac's law is strictly accurate must be defective. 

 The physical method cannot lead to the same result 

 as the chemical until a correction is introduced, and 

 then the discrepancy is found to disappear. One 

 svstematic way of making this correction has been 

 devised and used by M. Daniel Berthelot, and another 

 by M. Guye. 



Berzelius was led into a grave numerical error by 

 his unqualified acceptance of Gay-Lussac's law. In 

 NO. 2087, VOL. 81] 



the year 1819, in conjunction with Dulong, he deter- 

 mined the atomic v\'eight of carbon by the physical 

 method. The process adopted was to weigh a certain 

 bulk of carbon dioxide and subtract the weight of the 

 same bulk of oxygen. The difi'erence is the weight of 

 the carbon, on the incorrect assumption that carbon 

 dioxide contains exactly its own bulk of oxygen. The 

 atomic weight was found to be 7644 (0=ioo) or 

 i~'23 (0 = i6). This datum, which as a matter of fact 

 is much too high, was long used in chemistry. 

 Berzelius should not have fallen into this error, for lie 

 had received a warning two years before against the 

 danger of the physical method. He had determined 

 the atomic weight of sulphur by an experiment, similar 

 to the carbon dioxide one, with sulphur dioxide, and 

 he set aside the result, whicfi was I03"35 (0=ioo), 

 because it differed so much from the figure, ioo'7, 

 which he had obtained by a chemical method. 



Dumas and .Stas found it necessarv, in the year 

 1S39, to embark on a re-investigation' of the atomic 

 weight of carbon. Dumas had been analysing the 

 hydrocarbon naphthalene, and had obtained the 

 anomalous result, again and again, that the per- 

 centages of carbon and hydrogen added up to much 

 more than 100. ."Vs a result, the atomic weight of 

 carbon was found to be 7500, instead of 7644, as 

 Berzelius had said. 



This was a severe blow to Berzelius. He had 

 endured many reverses. One cherished conviction of 

 his had gone after another. Chlorine and nitrogen 

 had proved to be elements and not compounds of 

 oxygen, the " volume-theory " had become untenable, 

 his electrochemical theory was undermined, and his 

 system of chemistry was threatened by Gmelin. 

 Berzelius was yet the great master of atomic-weight 

 determination. Even that satisfaction was now denied 

 him ; none of his atomic weights was to be above 

 suspicion any longer, all because he had made an 

 unjustified use of Gay-Lussac's law, twenty years 

 before. There is a strange irony in the difficulties in 

 which Berzelius involved himself time and again by 

 his use of this law, in view of the protest he had made 

 against Dalton's refusal to accept it. 



A. N. Meldkum. 



ANEMOGRAPHIC OBSERVATIONS IN INDIAA 

 ]\/f OST of these memoirs are by the late Sir John 

 '■'-'■ Eliot, whose loss, while he was still capable of 

 much useful work, all meteorologists deplore. They 

 deal with the changes in wind direction and force at 

 the stations, showing both the diurnal and the 

 seasonal variations, and form a store-house of in- 

 formation for anyone who wishes to study the Indian 

 monsoons. 



Saugor Island is situated in the north-west of the 

 Bay of Bengal on the coast, about sixty-five miles in 

 a direct line from Calcutta, and ninety if the bends of 

 the river are followed. The land around it is perfectly 

 flat, and only a few feet above the sea, so that the 

 exposure is an excellent one. 



The land at Alipore is also flat, but there are many 

 trees in the district the tops of which are level with or 

 above the anemometer. As might be expected, the 

 winds are far stronger at the coast station. 



.Saugor Island lies in the track of the circular storms 

 (cyclones) of the Bay of Bengal, and it is of interest 

 to compare the maximum hourly velocity in these 



1 A Discussion of the Anemographic Observations recorded at Sanger 

 Island from March, 1880, to February. 1904. Also at .-Mipore, Calcutta, 

 from March, 1877, to February, 1904. Vol. xvlii., part ii. Also at Pach- 

 mark from September, 1883, to April, 1887. Also at Nagpur from January, 

 1S82, to December, 1902. Vol. xlx., part i. At Roorkee from September, 

 1879, to August, 1904. At Lahore from January, 1S89, to May, 1905. At 

 Mussoorie from May to October, 1877 to 1888. (London : Harrison and 

 Sons.) 



