

i P 



6G4 



REPOllT — 1881. 



I I 



i 



indifjo hy Bnoyev, and lustly tlu' pvoparation })y Fischer, of Iciiirinc, a ft'Lvifii^^o as 

 potent as quinine, are some of the well-known recent triunipli.s of nimlern syiitlnti- 

 cal chemistry. And tliese triiiniplis, h't us renieni))er, hiwe not heen ohtuined liv 

 any sncli ' randoiu liaphazardinf;' as yielded results in Priestley's time. In th',. 

 virgin soil of a century ajro, the prround only rerjuired to he scratched and the mviI 

 thrown in to yield a fruitfid croj); now the suifaco soil has lonj; heen exhausted, 

 and the successful culti\ator can f)nly olitain results hy a deej) and tli(jroii -li 

 preparation, and by a systematic and scientilic treatment of his material. 



Jn no department of our science has the protrress mad(> heen more important 

 than in that concerned with the accurati^ determination of the numerical, ])hysi(a!, 

 and chemical constants iipmi the exactitude of which every quantitative cliemieal 

 operation deptuids. For the foundation of an accurate knowled^'o of the first of 

 theP(> constants, viz., tlie ato.nic weii^hts of the eienienis, science is indebted to the 

 indefati^rahle labours of Berzelius. iJut ' humanum est orrare,' and even Berzeliiis' 

 accui'ate hand and d(dicate conscientiousness di<l not ]n'eserve him from mistaliej, 

 since corrected l)y other workers. In such determinations it is dillicult if not im- 

 possible always to ascertain the limits of error attachinjr U) the number. The 

 errors may he due in the first place tomanipulati^•e faults, in the second to inaccurncy 

 of the methods, or lastly to mistaken views as to the compositidu of tlio niati'iial 

 operated upon ; an<l hence tlu^ uniformity of any series of similar deti'miinatimis 

 p;ive3 no jriiarantee of tlieir trutli, the only safe f^uide being the agreement of 

 (h'iterminations made by altogether different methods. The work commenced by 

 T?erzelius has heen worlhily continurd by many cluunists. 8tas and Marignae, 

 bringing worlv of an almost astronomical accuracy into our science, have ascertained 

 the atomic weiglits of silver ami iodine to within oni^ hundri'd-thousandth of tlicir 

 value, whilst the nundjers for chlorine, bromine, potassium, sodium, nitrogen, sul- 

 phur, and oxygen may now be considered correct to within a niut in tlie fourth 

 figure. Few of the elements, however, boast nund)ers approaching tliis degree of 

 accuracy, and numy may even still be erroneous, from half to a whole unit of 

 hydrogen. And (as Lothar .Meyer says) until tlie greater number of the atomic 

 weights are determined to within one or two tenths of the unit, we cannot ex])ect 

 to be able to ascertain the laws which certainly govern these numbers, or to 

 recognise the relations wliich imiloubtedly exist between them and the general 

 chemical and pliysical properties of the elements. Among.st the most interesting 

 recent additions to our knowledgt> nui(h> in this de])artment we may note the 

 classical exnerinu'uts, in ]880, of J. W. Mallet on aluminium, and in the same 

 year of J. 1*. Coolce on antimony, and those, in the present year, of Thorpe on 

 titanium. 



Since the date of IVrzelius' death to the present day no discovery in our 

 science has been so f'ar-reaclnng, or led to such unforeseen and remarkable con- 

 clusions, as the foundation of Spectrum Analysis by Ihinscn and KirchholTin l^tlO. 



Independently altogetlu'r of the knowledge which has been gained concerning 

 the disti'ihution of the elementary bodies in terrestrial matter, and of the dis- 

 covery of half-a-<Iozen new elements by its means, and putting aside for a nidment 

 the revelation of a chemistry not hounded by this world, but limitless as the 

 heavens, we find that over and above all these results spectrum analysis offers the 

 means, not otherwise open to us, of obtaining knowledge concerning the atomic and 

 molecular condition of matter. 



T^et me recall some of the more remarkable conclusions to which the researches 

 of Lockyer, Schuster, Jiiveing and Dewar, Wiillner and others in this direction 

 have led. In the first place it is well to hear in mitid that a difference of a very 

 marked kitid, first distinctly pointed out by Alex. ]Mitscherlich, is to be observed 

 1)etween the spectrum of an element and that of its compounds, the latter only 

 lieing seen in cases in which the compound is not dissociated at temperatures neces- 

 sary to give rise to a glowing pas. Secondly, that these compound spectra— 

 fis, for instance, those of the halogen compomids of the alkaline-earth metals— 

 exhil)it a certain family likeness, and show signs of systematic variation in the 

 position of the lines, corresponding to changes in the molecular weight of the 

 vibrating system. Still this important subject of the relation of tbe spectra of 



