June 29, 1888.] 



SCIENTIFIC NEWS. 



615 



generally found worthless. The ores contain from 1 to 

 10 percent, of copper, but they are more especially in 

 request as sources of sulphur for the manufacture ot 

 sulphuric acid. 



Modern Science in Bible Lands. By Sir J. W. Dawson, 

 C.M.G., LLD. F.R.S., etc. London: Hodder and 

 Stoughton. 1888. 



In his introductory remarks Sir William Dawson says 

 that the special object of his new work is "to notice the 

 light which the scientific exploration of the countries of 

 the Bible may throw on the character and statements of 

 the book." The author's position as a geological observer 

 of high repute gives authority to his statements regarding 

 matters of geological fact and hypothesis ; and his 

 researches are rendered very interesting from their 

 connection with the records of the Hebrew Scriptures; 

 but notwithstanding all the points telling in its favour, we 

 cannot help entertaining the opinion that the book would 

 have been more valuable had its tone savoured less of 

 polemic and controversy. It contains, in fact, too much 

 pseudo-theological argument, and is too obviously a work 

 " with a purpose." 



These characteristics prevent our reviewing it in 

 detail, for they necessarily carry it outside the range of 

 ordinary scientific criticism ; but we gladly bear 

 testimony to the clearness and felicity of style with 

 which the subject is treated, as well as to the admirable 

 way in which both printer and publisher have done 

 their duty. 



A Feiv Words on Portland Cement. By a Manufacturer. 

 D. L. Collins (of Gibbs and Co., Limited). Second 

 edition. With Appendix on the Relation of 

 Chemical Analysis to Quality in Portland Cement. 

 London and New York : E. and F. N. Spon. 

 The use of Portland cement in engineering construc- 

 tions, whether civil or military, has very much increased 

 of late, and is likely to extend still further. The author 

 of this little treatise is evidently the first manufacturer 

 who has made public the results of his experience, show- 

 ing what conditions are necessary for the production of a 

 thoroughly good qualitj', and explaining the value and 

 the application of the usual tests. 



The scope of chemical analysis is limited, since two 

 samples, one good and the other bad, may differ respec- 

 tively very little in their percentage composition. It is, 

 however, necessary to ascertain whether the original pro- 

 portion of lime employed is excessive, and whether any 

 of it remains in the free state, i.e., not chemically combined 

 with silica and alumina. The proportion of carbonic 

 anhydride, or carbonic acid, as it is more popularly 

 called, should never exceed i"5o per cent. The highest 

 figure we find in the analyses quoted is i"i4 per cent. 

 Any excess of sulphur or of magnesia is also highly 

 objectionable. 



Mention is made of a " slag cement," which is a 

 mechanical mixture of ground iron slag with slacked 

 lime. This mixture, which is sometimes sold as such, 

 and sometimes used for adulterating Portland cement, 

 is considered by the highest engineering authorities to 

 be inferior in quality. Directions for the detection of this 

 slag cement are here given. 



Mr. Collins deserves great credit for having departed 

 from old rule-of-thumb routine, and for the public spirit 

 which he has shown in laying the results of his ex- 

 perience before the world. 





ROYAL SOCIETY. 

 At the meeting on June 15th the following communica- 

 tions were read: — "The Electric Organ of the Skate," 

 "Structure and Development of the Electric Organ 

 of Raia Radiata" by J. C. Ewart, M.D., Regius Pro- 

 fessor of Natural History, University of Edinburgh. Com- 

 municated by Prof. J. Burdon Sanderson, F.R.S. 



The first part of this paper is chiefly devoted to a 

 comparison ot the electric organs of Raia radiata, R. 

 batis, and R. circidaris. In the first place it is shown 

 that the organ in Raia radiata is absolutely and rela- 

 tively of less dimensions than that of either of the other 

 two. In Raia radiata the electric cup -is little more 

 than a muscular fibre with one end expanded, the ex- 

 panded end being slightly excavated to support a greatly 

 enlarged motor plate, in which terminate numerous 

 nerve fibres. It thus only remotely resembles the well- 

 formed electric cups of Raia circularis. The median 

 striated layer of the other two species is absent in Raia 

 radiata, and the electric layer is indistinct. 



The second part of the paper deals with the develop- 

 ment of the electric cups of Raia radiata. It is shown 

 that the rate of development compared with the other 

 two species is extremely slow, the organ being scarcely 

 completed when the skate has reached its full size. 



The comparison, therefore, tends to show that the 

 organ of Raia radiata is in the process of development. 



" The Minimum Point of Change of Potential of a 

 Voltaic Couple." By Dr. G. Gore, F.R.S. 



In this communication is described the following very 

 simple method of detecting the influence of the minimum 

 proportion of chlorine or other soluble substance, etc., 

 upon the electro-motive force of a voltaic couple (^Nature, 

 vol. 38, p. 17). 



Take a voltaic couple, composed of an unamalgamated 

 strip of zinc or magnesium (the latter is usually the most 

 sensitive), and a small sheet of platinum, immersed in 

 distilled water ; balance its electric potential through an 

 ordinary galvanometer of about 100 ohms resistance by 

 that of a precisely similar couple, composed of portions 

 of the same specimens of the same metals immersed the 

 same moment as the other pair in a separate quantity of 

 the same water, and gradually add to one of the two 

 cells sufficiently small and known quantities of an 

 adequately weak solution of known strength in a portion 

 of the same water of the substance to be used, until the 

 balance is. upset, and take note of the proportions of the 

 substance and of the water then contained in that cell. 

 In the present experiments a magnesium-platinum 

 couple was employed. 



The minimum proportions required^ with several 

 substances were as follows : — Potassic chloride between 

 I part in 3,875 and 4,650 parts of water; potassic 

 chlorate between i in 4,650 and 5,166; hydrochloric 

 acid, between i in 516,666 and 664,285 ; and with chlo- 

 rine, between i in 15,656,500,000 and 19,565,210,000. 



The proportion required of each different substance is 

 dependent upon very simple conditions, viz., unchanged 

 composition of the voltaic couple, a uniform temperature, 

 and employing the same galvanometer. The apparently 

 constant numbers thus obtained may probably be used 



