336 



NATURE 



{Feb. 15, 1877 



Unio were found, making six in all, now known to occur 

 in these strata. 



" They are all of either distinctively American types or 

 closely related to species now livingin American fresh waters. 

 They represent by their affinities the following living spe- 

 cies : — Unio ciavus, Lamarck ; U. securis, Lea ; U. gib- 

 bostis, Barnes ; U. metaneorus, Rafinesque ; and U. com- 

 planatus, Solander. They are associated in the same 

 stratum with species of the genera Corbula, Corbicula, 

 Neritina, Viviparus, &c., and which stratum alternates 

 with layers containing Ostrea and Anomia. The close 

 affinity of these fossil Unios with species now living in 

 the Mississippi river and its tributaries, seems plainly 

 suggestive of the fact that they represent the ancestry of 

 the living ones. An interesting series of facts has also 

 been collected, showing that some of the so-called Ameri- 

 can types of Unio were introduced in what is now the 

 great Rocky Mountain region as early as the Jurassic 

 period, and that their differentiation had become great 

 and clearly defined as early as late Cretaceous and early 

 Tertiary times. Other observations suggest the probable 

 lines of geographical distribution, during the late geologi- 

 cal periods of their evolutional descent, by one or more 

 of which they have probably reached the Mississippi 

 river system, and culminated in the numerous and diverse 

 forms that now exist there. 



" The work of the past season shows very clearly the 

 harmonious relations of the various groups of strata over 

 vast areas, that although there may be a thickening or a 

 thinning put of beds at different points, they can all be 

 correlated from the Missouri river to the Sierra Nevada 

 basin. The fact also that there is no physical or palason- 

 tological break in these groups over large areas from the 

 Cretaceous to the Middle Tertiary, is fully established. 

 The transition from marine to brackish water forms of 

 life commences at the close of the Cretaceous epoch, and 

 without any line of separation that can yet be detected,con- 

 tinues on upward until only purely fresh-water forms are 

 to be found. Dr. White, an eminent palaeontologist and 

 geologist, says that the line must be drawn somewhere 

 between the Cretaceous and Tertiary epochs, but that it 

 will be strictly arbitrary, as there is no well-marked phy- 

 sical break to the summit of the Bridger group." A. G. 



ALLOY OF PLATLNUM AND IRIDIUM FOR A 

 NEW METRIC STANDARD OF LENGTH 



THE Warden of the Standards has, in his valuable 

 annual reports, described the steps which have been 

 taken to secure new International Metric Standards, and 

 Mr. Chisholm has also given abundant information as to 

 the various points of interest connected with their prepar- 

 ation and preservation. The advantage of employing an 

 alloy of platinum and iridium appears to have been so con- 

 clusively demonstrated that the French Chamber granted, in 

 November, 1875, 260,000 francs (10,400/.) for the expenses 

 of constructing the new International Prototype Standards, 

 and, of this sum, 257,500 francs were required for the cost 

 of an alloy containing 90 per cent, of platinum, and 10 per 

 cent, of iridium, of which they were to be made.^ 



The preparation of a bar for a standard of length has 

 been undertaken for the Association Gdodesique Inter- 

 nationale by Messrs. Johnson, Matthey and Co., who pre- 

 sented the results of their labours to the Academie des 

 Sciences on December 4 last.^ The platinum and iridium 

 used were prepared by the processes of MM. St. Claire 

 Deville and Debray, and they were analysed in their labora- 

 tory before fusion. Mr. George Matthey thus describes the 

 method by which this difficult task was accomplished. Five 

 ingots were prepared by melting together in each case 450 

 ounces of platinum and 55 ounces of iridium. These were 

 then cut in small pieces by the aid of an hydraulic press, and 

 the fragments melted together and kept fluid by a flame 



^ Tenth Annual Report of the Warden of the Standards, 1876, p. xxxiv. 

 - Coinptcs Reiidus, No. 23, 1876, p. 1,090. 



of coal gas and oxygen. The ingot obtained was lami- 

 nated, cut into strips, and again melted into an ingot, 

 which appeared to be very homogeneous and free from 

 roughness or visible flaws. This ingot was forged into a 

 bar 35 cm. long, 7-5 cm. wide, and 2-5 cm. thick. The 

 greater part of this was repeatedly annealed and rolled 

 between polished cylinders of steel until it was 4'io 

 metres long, 21 mm. wide, and 5 mm. thick, which were 

 very nearly the required dimensions. Then a perfectly 

 rectangular form was imparted to the rule by means of a 

 "drag-bench," and the finishing was effected by a planing 

 machine, as the alloy, owing to its extreme hardness, re- 

 moved iron from the plates through which it was drawn. 



After Mr. Matthey's communication had been read, M. 

 St. Claire Deville gave the result of a careful examination 

 to which he had submitted the bar. He found that the 

 alloy in the form of an ingot has a density 21*508 at 0° C, 

 an oblong mass cut from the bar, was found to be, after 

 annealing, of the density 21 "5 16, which showed that when 

 annealed, at a high temperature, the metal assumes very 

 nearly the density of the fused metal. It was proved by 

 analysis to contain — 



I. II. 



Platinum ... ... ... 89'40 ... 89*42 



Iridium ... iO'i6 ... 1022 



Rhodium ... ... ... -iS ... '16 



Ruthenium ... ... .. 'lo ... "lo 



Iron '06 ... -06 



99 "90 ... 99*96 

 From which the following figures were deduced : — 



Proportion. ^^J'c^ Volume. 



Platinum Iridium at 10 per cent. 99'33 21 "575 4'6o3 



Iridium in excess 0*23 22"38o o"oio 



Rhodium o'i8 i2"ooo o'oi5 



Ruthenium , ... o'lo I2"26i 0008 



Iron o'o6 7700 0"oo8 



99-90 4-644 



Density at 0° C. calculated from analysis No. I. = 21-510 

 „ „ „ No. IL = 21-515 



which agree perfectly with the results of the analyses, 

 and with regard to them it should be pointed out, that it 

 is very difficult to purify platinum and iridium, and that 

 the smallness of the amounts of rhodium and ruthenium 

 present affords additional evidence of the care with which 

 the refining was performed. It is well known that all 

 substances capable of being tempered, such as glass and 

 steel, change their dimensions in time, others which be- 

 come crystalline with changes of temperature, as zinc does, 

 are in the same case. The researches of Mr. Wild have 

 shown that hyalite, a variety of opal, appears to be free 

 from this mobility of form, and consequently of density. 

 With facts such as these in view, M. St. Claire Deville 

 proposes to make certain experiments in conjunction with 

 M. Mascart, to determine whether platinum-iridium is 

 subject to a permanent change of volume or not. 



The work upon which the accuracy of standards depends 

 is of the highest importance, and Mr. Matthey has well 

 sustained the reputation of this country for technical skill. 

 Metallurgists will appreciate his success, for they can 

 recognise the difficulty he has had to contend with in the 

 fusion and working of such an alloy, but for those who are 

 less familiar with the conditions which had to be met, we 

 would quote the graceful words of MM. Dumas and 

 Deville. The former observed : " II a execute ce travail 

 avec un succes complet sous le double rapport de la com- 

 position exacte de I'alliage et de la forme de la regie .... 

 I'interet actuel est dvident, et la production enrichit I'outil- 

 lage scientifique d'un alliage dou^ de projJri^tds pr^cieuses." 

 M. Deville said : " Qu'il me soit permis, en terminant, de 

 remercier le mdtallurgiste habile, le savant distingue, M. G. 

 Matthey, qui a accompli son oeuvre avec un talent et un 

 ddsintdressement qui ne seront pas perdus pour la science." 



W. Chandlicr Roberts 



