April, 1915. 



KNOWLEDGE. 



101 



state of purity, would afford much more exact 

 data for the determination of the atomic weight 

 than the chemical method. If we consider that 

 even in the case of an element whose atomic weight 

 has been determined repeatedly with the utmost 

 care — say silver or chlorine — the result is not 

 certain to one part in three thousand, whereas the 

 wave-length of a line can be measured with an 

 accuracy of one part in one hundred thousand, 

 we see how important the spectroscopic method 

 might become. 



The diagram Figure 79 is drawn to exhibit a 

 relationship between oscillation-frequencies and 

 squares of atomic weights. It will be easily under- 

 stood that, if this relationship were exact, we could 

 calculate the atomic weight of one of the three 

 elements from those of the other two — say the 

 atomic weight of rubidium — from those of caesium 

 and potassium, 132-81 and 39-10 respectively. 

 Making the calculation for each set of homologous 

 lines m=3, m=\, ;« = 5, and so on, we obtain for 

 the atomic weight of rubidium numbers increasing 

 gradually (but slightly) up to the convergence- 

 frequency, of which a few examples are given. 



4 gives the at. wt. of rubidium as 85-047 



85-575 

 85-943 

 86-060 

 85-814 

 85-830 

 86-141 

 86-069 

 Mean 85-31. 

 The recognised atomic weight is 85-45. 



It will further be remarked that in the diagram 

 the connecting-lines seem to intersect on the line 

 of zero atomic weight ; or, in other words, the 

 separations of the pairs of lines are proportional 

 to the squares of atomic weights. Thus for the 



red pairs we have 



Wave-lengths. 

 D . - f 7699-23 



Potassium • n cc~ nn 



[_ 766o-27 

 / 7949-04 

 i 7803-17 

 I 8949-92 

 I. 8527-72 

 From the proportion Rb 2 : C< 



Rubidium 



Caesium 



Oscillation- Differ- 

 frequencies. 



12984-81 , 



13042-35 .1 



12576-74 i 



12807-17 J 



11170-26 



11723-26 

 2 =230-43 : 553-00 we 



ence. 



57-54 



230-43 



} 553-00 



get for rubidium 85-73 when C?= 132-81. 



(To be continued.) 



ON THE FORMATION OF HAIR PIGMENT. 



By H. ONSLOW. 



The histological formation of the hairs of certain 

 animals and the condition in which the pigment 

 is present in them were described in an earlier 

 communication.* We must now inquire into the 

 processes involved in the production of this pigment. 

 The earliest investigators were of the opinion that 

 the melanins, or dark pigments of the skin and hair, 

 had their origin in the blood, as is the case with 

 the bile and certain other body pigments. There 

 was, however, little or no evidence on which to 

 base such a theory, except the fact that it was found 

 that the weight of iron contained in the ash of 

 negroes' skin was twice as great as that of the white 

 man's skin, and other equally inconclusive evidence. 

 It is now known that the keratin of the skin 

 and hair contains a certain quantity of iron, 

 which is not, however, a necessary component 

 of the melanin molecule, and has no connection 

 with the iron of haemoglobin. The theory that these 

 pigments were derived from the blood received its 

 death-blow with the discovery that the sap of the 

 Japanese lacquer-tree, described by Yoshida, con- 

 tained a ferment capable of oxidising a certain 

 phenolic substance or chromogen to the black 

 lustrous pigment which composes the surface of 

 Oriental lacquer. Shortly afterwards, the further 



discovery that this oxidising ferment was widely 

 distributed throughout both the vegetable and 

 animal kingdoms served to form the foundation of 

 the modern oxydase theory of pigment formation. 

 Many of these ferments, called laccases, have the 

 power of oxidising some phenolic substances, 

 especially those containing several hydroxyl 

 groups, to products varying in colour from 

 yellow to black. Others, the so-called tyrosinases, 

 oxidise solutions of the amino-acid tyrosine, 

 as well as many polypeptides, containing tyrosine, 

 which are changed through red to violet, and 

 yield finally a black precipitate. A plausible 

 theorv for the production of many animal 

 pigments is suggested by the fact that phenols 

 {e.g., p-cresol) in the presence of amino com- 

 pounds may be made to show an almost infinite 

 variety of colours by suitably varying the phenol 

 and amino components. 



In the vegetable kingdom these ferments are 

 found in a number of fungi, in potatoes, and in many 

 roots. Among animals they are found in the 

 body-filling of meal-worms, in the larvae of many 

 insects, and in the pigment sac of the cuttle-fish, 

 where they give rise to sepia. Among vertebrates, 

 also, both tyrosinase and tyrosine are found in 



"Knowledge," Volume XXXVII, page 161 (May, 1914). 



