54 



NATURE 



\Nov. 19, 1874 



would obtain the weight of the atom of sulphur compared 

 to hydrogen as the unit. The specific gravity he obtained 

 was about i'23— corresponding nearly, he says (p. 451) 

 to Thdnard's number, 1-23. Hence (as he believed air to 

 be twelve times as heavy as hydrogen) he v/ould obtain 

 the atomic weight of sulphur as (t2 X r23) - i = 1376, 

 which number, standing half way between I4"4 as given in 

 the first table, and 13 as given in the second, points out 

 the origin of the first relative weight of the ultimate 

 particle of sulphur. So from sulphurous acid he would 

 obtain a similar number, taking the specific gravity as 

 obtained by him (Part ii., 389) to be 2-3, and remembering 

 that this gas contains its own bulk of oxygen (p. 391), he 

 obtained (2-3 - ri2) X 12 = 14-16 for the atomic weight 

 of sulphur. As, however, we do not possess the exact 

 numbers of his specific gravity determinations, and as we 

 do not exactly know what number he took at the time as 

 representing the relation between the densities of air and 

 hydrogen (in 1803 he says that the relation of i : 0^077 is 

 not correct, and that ^^ is nearer the truth), it is impossible 

 to obtain the exact numbers for sulphur as given in the 

 first table. 



In reviewing the experimental basis upon which Dalton 

 founded his conclusions, we cannot but be struck with the 

 clearness of perception of truth which enabled him to 

 argue correctly from inexact experiments. In the notable 

 case, indeed, in which Dalton announces the first instance 

 of combination in multiple proportion (Manch. Mem. 

 vol. i., series ii., p. 250), the whole conclusion is based 

 upon an erroneous experimental basis. If we repeat the 

 experiment as described by Dalton, we do not obtain the 

 results he arrived at. Oxygen cannot as a fact be made 

 to combine with nitric oxide in the proportions of one to 

 two by merely varying the shape of the containing vessel ; 

 although by other means we can now effect these two 

 acts oi combination. We see, therefore, that Dalton's 

 conclusions were correct, although in this case it appears 

 to have been a mere chance that his experimental results 

 rendered such a conclusion possible. 



INTERNA TIONAL METRIC COMMISSION A T 

 PARIS 



'"PHE Permanent Committee of the International 

 -'- Metric Commission, elected from among the mem- 

 bers at their general meeting at Paris, in 1872, has just 

 concluded a series of meetings, the first of which was 

 held on October 6. The Committee were directed to 

 meet at least once a year, in order, amongst other 

 things, to examine the progress of the work of the French 

 Section, to whom the construction of the new standards 

 was entrusted, with a view to the concurrence of the 

 Committee as the executive organ of the Commission. 



At their recent meetings, the Committee fully considered 

 and discussed a detailed report of the proceedings of the 

 French Section since the melting of the great ingot of plati- 

 num-iridium on May 13 last, from which all the new Inter- 

 national Metric Standards are to be made (an account of 

 which was given in Na TURK, vol. x. p 130) ; and, generally 

 speaking, the Committee expressed their unanimous 

 concurrence and satisfaction at the mode in which the 

 French Section have hitherto executed the duties entrusted 

 to them by the Commission, and they also gave their 

 decisions on certain points submitted to them for the 

 guidance of the French Section in their future operations. 

 The first operation to which the great ingot of 250 kilo- 

 grammes of platinum-iridium was submitted, when in its 

 rough state, and cleansed from all extraneous matter, was 

 to have all the inequalities on its surface, that had been in 

 c intact with the lime of the calcined furnace, removed 

 v.itli a cold chisel. The ingot with its surface thus 

 moothed was found to weigh 236'33o kilogrammes. 

 I 1 this state it was e.Khibited to the Academic des 



Sciences at their scaiiu of July 2, 1874. A portion of 

 this large homogeneous mass of metal, when analysed 

 by M. Henri Saint-Claire Deville, showed the proportion 

 of iridium to be io'29 per cent. 



The ingot v/as next forged by M. M. Farcot under a 

 steam hammer weighing 5,000 kilogrammes, until by suc- 

 cessive hammerings and annealings, in a single day, it was 

 brought to the form of a bar five centimetres square in 

 section. By similar operators this bar, divided into con- 

 venient lengths, was afterwards further reduced to eight 

 bars 2"5 centimetres square in section, and of a total 

 length of i6'4o5 metres. 



A remarkable phenomenon was observed by M. Tresca 

 during the forging of these bars, and was communicated 

 by him to the Academic des Sciences at their stance of 

 July 9. At the moment when the hammer struck the 

 bar, lines of light were seen to pass downwards from the 

 edges of the hammer, and to cross each in the form of 

 an X on each of the side surfaces of the bar. These 

 lines continued afterwards distinctly visible in a certain 

 light, appearing like slightly burnished marks. 



The next operation was to prepare the bars for drawing 

 into the X forin, by cutting longitudinal grooves along 

 the middle of each of the foiu- sides of the bars by means 

 of a planing machine. A further object of cutting these 

 grooves was to ascertain if there were any flaws on the 

 surface of the metal so exposed, as it was found absolutely 

 necessary to remove any such flaws, else they would 

 remain as blemishes on the surfaces of the bars when 

 drawn. 



The eight bars were next submitted by M. Gueldry, 

 at the Audincourt foundry, to successive operations of 

 drawing out and annealing, until they were accurately re- 

 duced to the X form of the Tresca section, when each was 

 extended to a length sufficient to make three or four 

 metre bars. The first of the grooved bars was passed 

 through the dies no less than 220 times, and was as often 

 suljjcctcd to annealing. It was afterwards ascertained 

 that the rigidity of the drawn bars was but little affected 

 by the process of annealing, their co-efficients of elasticity 

 being found as follows : — 



Before annealing ... ... 2r2o85 



After annealing ... ... ... 2i'oo73 



Their co-efficient of expansion was also found to be but 

 very slightly changed, and in the opposite direction, viz. — 



r> ec • ^ r — • c 'r*. . " r' Variation for 



Co efficient of expansion for i L. at mean t. 40 C , p 



Before annealing o'oooooSSo,2 0,84 



After annealing 881,9 Oj^S 



When divided into finished bars of the X section, 

 I '02 m. in length, each bar is made perfectly straight by 

 special arrangements contrived for this purpose. Four 

 straight edges of steel are made exactly to fit into the 

 grooves of the X bar, and to forrn, when so fitted, a 

 rectangular bar two centimetres square in section. This 

 squared bar is then enclosed between the plane surfaces 

 of four solid rectangular iron bars ; and all lacing tightly 

 compressed with iron clamps in the form of hollow 

 squares and with iron wedges, the whole is heated in a 

 furnace till red hot, when the clamps are further tightened 

 and the mass of metal is left to cool. By this operation, 

 each of the X metre bars is made perfectly straight. Up 

 to the present time bars of the X section have been made 

 sufficient for more than thirty metres. 



The polishing of the surface of the X bars next 

 follows. This is effected by the use of polishing powder 

 and powdered charcoal. Particular attention is given to 

 the polishing and subsequent burnishing of that portion 

 of the surface of the metal on which the defining lines 

 are to be cut. .Several experiments which have been 

 made tend to show that the best surface for cutting the 

 lines will be obtained by the final operation of slightly 

 impressing a stamp of highly polished steel, of the dimen- 

 sions of 3 mm. by 2 mm. By this means an identical 



