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NA TURE 



yjune 19, 1S84 



by introducing an argument which at once appealed to 

 the sympathy of the chemist, by showing that, if a mixture 

 of the iodides of two distinct radicles, such as ethyl, C 2 H 5 , 

 and butyl, CjHg, were submitted to the action of sodium, 

 a hydrocarbon was produced which consisted of ethyl and 

 butyl united together. There was no reason to suppose 

 that when a single iodide was thus treated the radicle 

 remained free, and Wurtz showed that the physical pro- 

 perties of the hydrocarbons produced from single iodides 

 were such as to prove that they were formed by the union 

 of two similar radicles, as on no other hypothesis could 

 they be ranged in a series with the hydrocarbons resulting 

 from the association of two dissimilar radicles. It was a 

 logical extension of this discovery to double the formula 

 of free hydrogen, a step which, indeed, Brodie had already 

 advocated, and which Frankland had clearly maintained 

 was an essential preliminary to the doubling of the 

 formulae of the organic radicles. Wurtz also pointed out 

 that the idea that the hydrogen molecule is compound 

 must be extended to other elements, and that generally 

 the simple bodies, like compounds, are composed of groups 

 of atoms, and react not by combining but by exchange of 

 elements. 



The number of elements of which the molecular weight 

 has been ascertained is, however, very small, and although 

 the idea thus put forward by Wurtz undoubtedly applies 

 to all the gaseous elements, and to bromine, iodine, sul- 

 phur, phosphorus, and arsenic, we now know that the 

 only metals of which the density in the gaseous state has 

 been satisfactorily determined, viz. mercury and cadmium, 

 form distinct exceptions to the rule ; we can therefore 

 draw no conclusions of any value as regards the molecu- 

 lar composition of the metallic elements. It is a striking 

 illustration of the slowness with which knowledge extends 

 into that lower stratum which is governed by the text- 

 books, that the view put forward by Wurtz, and which, 

 with the above-mentioned limitation, is so clearly justified 

 by facts, is almost universally disregarded by hand-books 

 of chemistry ; in fact, there is a most astounding super- 

 stition among students of chemistry that the elements 

 generally have diatomic molecules. 



In 1855 Wurtz was led by the brilliant experimental 

 results of Berthelot to discuss the formula of glycerin, 

 and he was the first to point out that this body is to be 

 referred to the type of three molecules of water ; that, in 

 f.ict, it can be regarded as an alcohol formed by the dis- 

 placement of three atoms of hydrogen in three molecules 

 of water by the radicle C 3 H 5 . Nearly all the alcohols 

 known at that time could be referred to the type of a 

 single molecule of water. Recognising the want of an 

 intermediate series of alcohols, Wurtz was led in 1S56 to 

 the discovery of the glycols, and in this case again his 

 work was of the highest value as a contribution to 

 chemical theory. 



Space does not permit of reference to the numerous 

 other investigations of Wurtz, many of which have exer- 

 cised an important influence upon chemical thought at 

 the time of their publication. Only one must be men- 

 tioned, as it may ultimately prove to have been the first 

 step towards the elucidation of the nature of the process 

 of digestion in plants and animals. The investigation 

 referred to is that on the sap of Carica papaya. He 

 showed that alcohol precipitates from this a body pre- 

 senting the characters of a strong digestive "ferment," 

 capable of dissolving moist fibrin in large quantities. 

 Experiments made with papaine, as the so-called ferment 

 is termed, appear to show that papaine begins by 

 combining with the " ferment," and that the insoluble 

 product then undergoes gradual change in contact with 

 water, the "ferment " being liberated and thus becoming 

 free to do new work. There is much to indicate that 

 mineral acids act in this way, and it is to be hoped that 

 the suggestion put forward by Wurtz will not long escape 

 notice, and that his investigation may be extended. 



AFRICAN EXPLORATION 



T ETTERS addressed to the Secretary of the Com- 

 ' mittee of the British Association for the exploration 

 of Kilimanjaro have just been received from Mr. H. H. 

 Johnston, dated from the British Residency, Zanzibar, 

 May 13. After consultation with Sir John Kirk, Mr. 

 Johnston had selected the Mombasa route for Kilima- 

 njaro, and was expecting to depart for that port in about 

 a fortnight's time. The country between Mombasa and 

 Chaga was said to be quiet, and to present no serious 

 difficulties in the way. Mr. Johnston had succeeded in 

 obtaining the services of three of the same bird-skinners 

 that had been employed by Dr. Fischer, and of a botanical 

 collector trained under Sir John Kirk, of whose kindness 

 and assistance he speaks in the highest terms. Mr. 

 Johnston, in spite of the trying climate of Zanzibar, was 

 in excellent health, and had strong hopes of the success 

 of the expedition. 



We are pleased to learn that Mr. Joseph Thomson has 

 arrived safely at Zanzibar from the expedition he under- 

 took to the Masai region. It will be remembered that Mr. 

 Thomson left England in the end of the year 1882, his 

 object being to proceed by Mount Kilimanjaro to the 

 almost unknown country of the Masai, and to settle the 

 question of the existence of a Lake Baringo to the east 

 of Victoria Nyanza. Mr. Thomson left Zanzibar in the 



spring of last year, but after proceeding some distance 

 found the country so disturbed owing to the recent pas- 

 sage of a German explorer, Dr. Fischer, that he was com- 

 pelled to return precipitately to Mombasa. In July last,, 

 however, he started again, and has evidently accomplished 

 his work in a way quite worthy of his previous record. 

 Passing round the north-eastern side of Mount Kilima- 

 njaro, Thomson proceeded north to Lake Naivasha, half- 

 way between Kilimanjaro and Mount Kenia ; then on to 

 the latter mountain, and by way of Lake Baringo to the 

 shores of Victoria Nyanza. This latter lake he skirted as 

 far as the outlet of the Nile, returning by a more northerly 

 route, striking the west coast of Lake Baringo, and pro- 

 ceeding south and south-east by Ukambani to Mombasa. 

 ! It is satisfactory to record that no lives have been lost 

 except by illness. The telegram which the Geographical 

 Society have received from Sir John Kirk does not, of 

 course, enter into minute details, but from its general tone 

 it is evident that Mr. Thomson will have an interesting 

 and instructive story to tell when he returns. The tele- 

 gram does not state positively that Mr. Thomson found a 

 lake where Baringo is placed on our maps, but as Ba- 

 ringo is mentioned as having been touched at, it seems 

 most probable that the information obtained from natives 

 by the sagacious Wakefield is correct. All the country 

 traversed by Mr. Thomson's expedition to the north of 



