December 17, 19 14] 



NATURE 



421 



is biconcave ; the ninth being invariably biconvex." 

 The same statement appears in the "Amphibia and 

 Reptile" volume of the Cambridge Natural History, 

 published some four years later (1901). 



So far as 1 am aware, exception has never been 

 taken to this statement. When, therefore, last year, 

 I had occasion to examine the vertebral column of 

 ^n Indian toad, Bujo melanostictus, I was surprised 

 to find that the eighth and ninth vertebrae were not 

 as described, but that, on the contrary, both were 

 proccElous, resembling in this the seven preceding 

 vertebrae. 



At first I supposed that this was merely an abnor- 

 mality' resembling the condition found by Lloj'd 

 Morgan in Rana tentPoraria in 1886, and recorded 

 by him in these columns (vol. xxxv., p. 53). I 

 examined, however, five other specimens of B. 

 ■melanostictus and also two of B. andersonii, and dis- 

 covered that, in every case, all the vertebrae were 

 procoelous, exactly as in my first specimen. 



I could only come to the conclusion that, in these 

 two species at least, we had exceptions to the rule 

 laid down in the works quoted. On my return to 

 England, therefore, I took an early opportunity of 

 consulting Mr. Boulenger upon this point, who very 

 kindly permitted me to examine a large collection of 

 skeletons of Bufo. 



Including my own specimens, more than fifty verte- 

 bral columns were examined, these belonging to some 

 forty different species of Bufo, and it then became 

 apparent that what I had been disposed to regard as 

 -an exceptional state of affairs, obtaining in a couple 

 of Indian toads, ivas actually an invariable condition, 

 and, moreover, one apparently diagnostic of the genus 

 Bufo, for not a single specimen showed either an 

 amphicoelous eighth or a biconvex ninth vertebra. 

 In every case the centrum of the ninth vertebra, 

 although hollow in front, has, of course, the usual 

 double convexit}- behind. 



Geo. E. Nicholls. 



Zoological Department, King's College, 

 London, W.C. 



A Lunar Halo. 



A REMARKABLE colourcd halo forming a complete circle 

 about the moon was witnessed by me on Wednesday 

 evening, December 2, at 7.15, my position being in 

 North Shields. I am seventy-nine years of age, and 

 never saw anything similar — that is, encircling the 

 moon. It only lasted about seven or eight minutes. 

 I am wondering if anyone else took much notice of it. 



An entire ring and colours were distinctly visible. 

 The inner part — that is, to the commencement of the 

 halo or rain-circle — had a remarkably globular appear- 

 ance, with the moon as an apex, and was the most 

 prominent part of the phenomenon. 



The moon at the time was very bright, but shining 

 through light fleecy clouds at a great height ; then the 

 yellowy appearance commenced as shown, terminating 

 with a dark orange rim. 



^ The altitude of the moon would be about 60°, direc- 

 tion S.E., wind W. 



Thos. Todd. 



26 Percy Square, Tynemouth, December 5. 



COLLOIDAL CHEMISTRY IN RELATION 

 TO INDUSTRIES. 



I. 



Al^fHEX the development of some branch of 



' ' science reaches the stage at which a 



separate literature with its own terminology 



NO. 2355, VOL. 94] 



begins to grow up, the question of its practical 

 utility or its value to the arts begins to be asked. 

 Whether research has to justify itself bv such 

 directly or indirectly useful results is at least 

 arguable, but it must be admitted that the ques- 

 tion is particularly natural when raised in con- 

 nection with a discipline like colloidal chemistry 

 which is concerned, inter alia, with substances 

 such as form the raw materials or the products 

 of important arts, many of which, like ceramics, 

 dyeing, tanning, the making of bread and of 

 fermented liquors, are as old as history. 



Where industries have empirically reached a 

 high degree of perfection, the chief function of 

 science is to provide the explanation of processes 

 which are the outcome of exjjerience, generally 

 with the result that improvements become possible 

 which experience alone cannot suggest. In 

 judging a new branch of chemistry it is too often 

 overlooked that even inorganic chemistry has 

 largely played this part and has not yet quite 

 succeeded in it in some respects : thus the theory 

 of a process as important and familiar as the lead 

 chamber process of making sulphuric acid is still 

 highly controversial. On the other hand, organic 

 chemistry provides many instances of the opposite 

 way in which science may assist industry : by pro- 

 ducing new bodies the properties of which are 

 anticipated on theoretical grounds. 



While, therefore, too much must not be ex- 

 pected of a science as young as colloidal chem- 

 istry, there is no doubt that it is destined to be 

 of considerable value to a great number of in- 

 dustries in both the directions indicated above. 

 Probably the most convenient method of showing 

 this will be to state, without undue technicalities, 

 a number of fundamental propositions which have 

 now been firmly established and to illustrate their 

 bearing on industrial processes and problems. 



There is an immense amount of material to 

 prove that the physical properties of a body may 

 be varied continuously between wide limits by 

 simply altering the size of its particles present 

 or — as it is technically called, "dispersed" — in 

 another medium, below a certain maximum limit. 

 This is strikingly the case with the most obvious 

 property, colour : thus, colloidal gold can be ob- 

 tained red, purple, blue, or green in solutions 

 containing the same amount of metal, and silver 

 solutions of the same concentration may range 

 from colourless through yellow, red, and purple 

 to blue. Colourless or slightly coloured sub- 

 stances, e.p. sulphur, may form brilliant blue 

 solutions. Solid colloidal solutions are also known 

 to exist, examples of which are ruby glass, 

 coloured by gold or copper, and the blue rock salt 

 occurring at Stassfurt, which is coloured bv 

 metallic sodium. 



The possibility of obtaining colour by dispersing 

 a colourless substance in a colourless medium has 

 been suggested as an explanation of the striking 

 tint of a very puzzling class of bodies, the arti- 

 ficial ultramarines. Their chemical composition 

 is very uncertain, but none of the compounds of 

 which thev are a mixture are at all likelv to be 



