822 PRINCIPLES OF CHEMISTRY 



thus the abnormal density of S 2 O 5 C1 2 remained unexplained until D P 

 Konovaloff (1885) showed that the previous investigators were working 

 with a mixture (containing SO 3 HC1), and that pyrosulphuryi chloride 

 has a normal density of approximately 107 Had not the law of 

 Avogadro-Gerhardt served as a guide, the impure liquid would have 

 still passed as pure ; the more so since the determination of the amount 

 of chlorine could not aid in the discovery of the impurity. Thus, by 

 following a true law of nature we are led to true deductions. 



All cases which have been studied confirm the law of Avogadro- 

 Gerhardt, and as by it a deduction is obtained, from the deter- 

 mination of the vapour density (a purely physical property), as to the 

 weight of the molecule or quantity of a substance entering into 

 chemical reaction, this law links together the two provinces of learn- 

 ing physics and chemistry in the most intimate manner. Besides 

 which, the law of Avogadro-Gerhardt places the conceptions of mole- 

 cules and atoms on a firm foundation, which Avas previously wanting. 

 Although since the days of Dalton it had become evident that it was 

 necessary to admit the existence of the elementary atom (the chemical 

 individual indivisible by chemical or other forces), and of the groups of 

 atoms (or molecules) of compounds, indivisible by mechanical and physi- 

 cal forces ; still the relative magnitude of the molecule and atom was not 

 defined with sufficient clearness. Thus, for instance, the atomic weight 

 of oxygen might be taken as 8 or 16, or any multiple of these numbers, 

 and nothing indicated a reason for the acceptation of one rather than 

 another of these magnitudes; 18 whilst as regards the weights of the 

 molecules of elements and compounds there was no trustworthy know- 

 ledge whatever. With the establishment of Gerhardt's law the idea of 

 the molecule was fully defined, as well as the relative magnitude of 

 the elementary atom. 



The chemical particle or molecule must be considered as the 



'8 And so it was in the fifties. Some took O = 8, others O = 16. Water in the first 

 case would be HO and hydrogen peroxide HO 2 , and in the second case, as is how gene* 

 rally accepted, water H 2 O and hydrogen- peroxide H 2 O 2 or HO. Disagreement and con- 

 fusion reigned. In 1860 the chemists of the whole world met at Carlsruhe for the purpose 

 of arriving at some agreement and uniformity of opinion. I was present at this Congress, 

 and well remember how great was the difference of opinion, and how a compromise was 

 advocated with great acumen by many scientific men, and with what warmth the followers 

 of Gerhardt, at whose head stood the Italian professor, Canizzaro, followed up the con- 

 sequences of the law of Avogadro. In the spirit of scientific freedom, without which 

 science would make no progress, and would remain petrified as in the middle ages, and 

 with the simultaneous necessity of scientific conservatism, without which the roots of 

 past study could give no fruit, a compromise was not arrived at, nor ought it to have 

 been, but instead of it truth, in the form of the law of Avogadro-Gerhardt, received by 

 means of the Congress a wider development, and soon afterwards conquered all minds. 

 Then the new so-called Gerhardt atomic weights established themselves, and in the 

 seventies they were already in general use. 



