February 16, 1SS3.] 



SCIENCE. 



45 



member is at once imparted to tlie standard bar, and 

 is so multiplied by delicate mechanism as to become 

 plainly Yisible. In testing a bridge, a movable index 

 upon the standard bar is first placed at zero. A load 

 is then run on to the bridge, when the index moves 

 oil account of the stretch imparted by the bridge to 

 the standard bar. The weight is now removed from 

 the bridge, when the index returns to zero unless the 

 iron has received a permanent elongation from the 

 load — that is, unless the iron has been overstrained. 

 Not only does this method enable us to determine 

 whether a bridge is safe for the time being; but we 

 can also answer the not less important question, 

 whether the bridge is holding its vitality through long 

 periods of time. The above apparatus is so delicate 

 as to indicate a strain on the iron less than a thou- 

 sandth part of the weight that would break it. By 

 means of this device, not only do we substitute exact 

 measurement for mere opinion, but we are enabled 

 to answer a good many vexed questions in regard to 

 the precise condition of complex structures of iron. 



G. L. V. 1101 



Cable power for street-railways. — There is 

 probably no more abused piece of motive power than 

 the horse which draws oiu- street-cars. Leaving out 

 of view the outrageous cruelty to which these unfortu- 

 nate animals are often subjected, it may well be ques- 

 tioned whether such power is in any way economical. 

 Whether steam or electricity will soon be employed 

 upon street railways, may be questioned ; but there is 

 reason to think that the so-called cable system may 

 furnish a solution to many of the problems in city 

 transportation. There is nothing new in the idea of 

 a continually moving, endless wire cable beneath the 

 roadway, to which cars maybe attached at any point; 

 but to reduce the idea to practice involves a good deal 

 of mechanical skill and a very considerable expense. 

 Mr. .J. D. Miller gives a description of the Chicago 

 cable roads, in which he states, that, in October last, 

 there were in Chicago over four miles of cable roads 

 in operation, — an amount which has been largely 

 increased since that time. The first cost of these 

 roads is reckoned to be not less than $100,000 a mile 

 for a double track. The cost of operation is said to 

 be much less than by the common method, the per- 

 centage of saving being greater as the trafiic becomes 

 largei". — {Journ. assoc. eng. .loc, Oct.) G. L. v. [102 



Tests of building materials. — An important 

 series of exjieriments upon the strength of timber 

 has been for some time past carried on by Professor 

 Gaetano Lanza at the institute of technology in 

 Boston, and also at the Watertown arsenal. The 

 experiments from which the data in our books have 

 been determined were in nearly all cases made upon 

 very small and very carefully selected pieces of well- 

 seasoned wood. From the data thus obtained we 

 have assumed that we could at once pass to the more 

 or less defective and generally quite unseasoned tim- 

 ber which is employed in actual work. This method 

 has often led to most absurd and unreliable results, 

 and has been a fruitful source of that discordance 

 which so often appears between science and practice. 

 Instead of small wooden beams an inch square and 

 two or three feet long. Professor Lanza uses beams 

 twenty feet long and of the common sizes used in 

 building ; and, instead of the perfectly clear and 

 well-seasoned material employed by the older experi- 

 menters, he takes his beams just as they come from 

 the lumber-yard. In fine, the experiments now being 

 carried on are as far as possible upder the real con- 

 ditions of practice, and not under the imaginary 

 conditions of the closet. The result of these experi- 

 ments will put into the hands of the engineer far 



better data for fixing the dimensions of tl)e important 

 structures on which our lives depend than we have 

 before possessed. — g. l. v. [103 



CHEMISTKY. 

 Reproduction of the osmides of iridium. — By 



heating iridium with iron pyrites, M. Debray obtained 

 it in octahedrons of the regular system, which were 

 removed from the sulphide by dissolving out the 

 latter with hydrochloric acid. Mixtures of iridium 

 and osmium treated in a similar manner gave regular 

 octahedrons which resembled in all respects the natu- 

 ral osmides. The natural osmides are thus shown 

 to be isomorphous mixtm'es, crystallizing probably 

 in the regular system. — (Comples rendus, xcv., 879. ) 

 c. r. M. [104 



Thorite and the equivalent of thorium. — In 

 a variety of thorite recently discovered at Arendal in 

 Norway, L. F. Nilson finds a large percentage of iron, 

 lead, and uranium, the latter in the form of dioxide. 

 To separate thorium from cerium oxide, after precipi- 

 tating the oxalates they were converted into sulphates, 

 and advantage was taken of the slight solubility 

 of hydrous thorium sulphate at 0°. In determining 

 the atomic weight of thorium, the purified sulphate 

 Th (So.,).,. 9 HjO was ignited at first gently to expel 

 the crystal water, then to a glowing white heat until 

 the acid was driven off. As a mean of ten determina- 

 tions calculated from the residue Th 0-2, the value 

 23.5.43 was obtained. The metal was prepared in 

 nearly the theoretical quantity by igniting potassium 

 thorium chloride mixed with a few grms. of salt, and 

 covered with sodium in a tube filled with salt. When 

 heated in a current of chlorine gas, the metal is con- 

 verted into the chloride. It unites readily with bro- 

 mine and iodine, and is easily soluble in acids. _ Under 

 no conditions does it decompose water, nor is it at- 

 tacked by alkaline hydrates. — (Beric/iie deutsch. 

 chem. r/esellsch.,-^Y.,2519.) c. F. m. [105 



Modification of the law of isomorphism.— 

 An examination of the isomorphous metatungstates 

 and tungstoborates, by D. Klein, led to resLilts which 

 could not be explained by the law of Mitscherlich. 

 A better interpretation was found in a modification 

 of the latter part of this law, first proposed by M. de 

 Marignac. "Isomorphous bodies either have a similar 

 cheniical composition, or they consist chiefly of the 

 same group of elements or of groups with identical 

 chemical functions." — {Comptes rendus, xcv., 7S1.) 



C. F. M. [106 



Electrolysis of hydrochloric acid. — In the 



electrolysis of hydrochloric acid, using platinum elec- 

 trodes, D. Tommasi finds that the heat absorbed in 

 decomposing two molecules of the acid amounts to 

 78.6 cal. Since platinitm, chloride was found in solu- 

 tion, a certain quantity of the electromotive force 

 (not determined) must have been absorbed in its for- 

 mation. One Uaniell's cell (E = 49 cal.) with one 

 zinc-cadmium element (E = 16.6) decomposed the 

 acid, but no chlorine appeared at the positive pole. 

 With two Daniell's cells, bubbles of an oxide of chlo- 

 rine were observed. When dilute hydrochloric acid 

 (1 cone, acid : 20 H.,0) was subjected to electrolytic 

 action, the liquid at the positive pole became yellow 

 and exerted a strong bleaching action. M. Tommasi 

 regards this action as due to the formation of hypo- 

 . chlorous acid which attacks the electrode in the con- 

 centrated acid solution. — (Comptes rendus, xcv., 689). 



C. F. M. [107 



Changes of volume and of molecular arrange- 

 ment in hydrous salts. — An imequal expansion 

 of the alums when heated led E. Wiedermann to con- 



