February 



1910] 



JVA TURE 



419 



turbances from a steady state of motion, and thus avoid 

 possible errors that may arise if one relies entirely on the 

 principle known as that of the " quasi-stationary state." 

 The method is explained in the first six sections, which 

 include the problem of initial uniformly accelerated motion 

 of a charged conductor of finite size, either from rest or 

 from uniform motion in a straight line. It appears that 

 the electric inertia calculated by this method does not 

 always agree with the value obtained from the energy of 

 a steady state. .As the results obtained include the case 

 of a conductor of small dimensions, several formulse are 

 compared with the experiments of Kauffmann on Becquerel 

 rays, and a fair proportion of inertia of ordinary kind is 

 found to be indicated by these experiments. .Application 

 of th method to uniformly accelerated linear and rotary 

 motion of insulators has been made. It is found that the 

 electric inertias for linear and rotary motions are the same, 

 provided half of it is located at the centre and half is 

 uniformly distributed over the surface of the spherical 

 body, supposed an insulator. Several sections deal with 

 vibratory motion of electrified systems. Some new features 

 connected with emission and absorption, and dependence 

 of frequency and damping on speed, are indicated. — H. 

 Thirkill : The nature of magneto-kathodic rays. In the 

 experiments described a variable longitudinal magnetic 

 field acts upon an electric discharge. The experiments 

 support the hypothesis that the luminous band, which, in 

 a strong magnetic field, follows the direction of the lines 

 of magnetic force and has the kathode for section, consists 

 of slowlv moving kathode rays. These have been bent by 

 the magnetic field into the form of a very fine spiral. The 

 charge was detected by using a sensitive galvanometer. 

 On this view, the following facts observed by Villard and 

 Righi are explained : — {\) the magneto-kathodic rays very 

 often appear quite suddenly, and (2) their appearance is 

 accompanied by an increased difficulty in detecting a 

 charge on them ; (3) the rays are deflected by an electric 

 field in a direction at right angles to the directions of both 

 the magnetic and electric fields ; (4) the distance the rays 

 extend from the kathode depends on the strength of the 

 magnetic field. The conclusion arrived at is that there 

 is not sufficient evidence to prove that the magneto-kathodic 

 rays constitute a new kind of rays. — E. Cunning-ham : 

 The velocity of steady fall of spherical particles through a 

 fluid medium. In view of experimental work on the fall 

 of small spherical particles through air, a discussion is 

 made in this paper of two of the main causes of deviation 

 from Stokes's law for the limiting velocity. The first 

 effect considered is that arising from the radius of the 

 particle being comparable with the mean free path of the 

 air molecules. The following modification of Stokes's 

 formula is obtained : — 



w/'l+J-^^')=6rMflV, 



where / is the mean free path of the molecules of air, 

 W is the weight, a the radius, and V the limiting velocity 

 of a falling particle, / being a fraction depending on the 

 nature of the surface of the particle, being unity for a 

 perfectly smooth elastic surface. For most actual cases / 

 probably lies between o and i. The formula agrees with 

 Zeleny's recent experimental verification that for particles 

 of radius greater than 10-* cm. the deviation found is not 

 large. The second effect discussed is that due to the 

 simultaneous presence of a large number of particles dis- 

 tributed throughout the fluid, assumed in this case to be 

 a continuous viscous medium. A formula is obtained which 

 indicates that, as the number of particles per unit volume 

 increases, the limiting velocity diminishes. The follow- 

 ing table gives the ratio of the estimated limiting velocity 

 (V) to that given by Stokes's law for different values of 

 the ratio of a, the radius of the particle, to b, the mean 

 distance between the centres of two adjacent particles : — 



Cqo 5-71 650 

 1-57 1-46 1-38 



8'i6 16-3 



hia i'63 2-45 3-26 4'o8 



VJ/V 7*29 3'o2 2"ro I "76 



— Dr. S. B. Schryver : The photochemical formation of 

 formaldehyde in green plants. On the additior of phenyl- 

 hydrazine hydrochloride, potassium ferricyanide and h5'dro- 

 chloric acid to solutions containing formaldehyde, a 

 fuchsine-like colour is developed, by means of which the 

 NO. 2IOI, VOL. 82] 



aldehyde, when present in small quantities, can be esti- 

 mated. The reaction can also be applied to the estimation 

 of formaldehyde when present in combination in such 

 substances as o.Kymethylene tetramine, if the reaction mix- 

 ture be boiled after addition of the phenylhydrazine reagent 

 and before the addition of the ferricyanide and hydrochloric 

 acid. By means of this method, formaldehyde can be 

 readily detected when present to the extent of only one 

 part in a million. The reaction has been applied to 

 demonstrate the presence of the aldehyde in chlorophyll 

 prepared from grass gathered after some hours of sun- 

 shine. The chlorophyll was extracted by alcohol, the 

 solvent was then evaporated off, and the residue re- 

 extracted with ether. In the product thus obtained, the 

 presence of the aldehyde could be demonstrated after warm- 

 ing it or allowing to stand for some hours with the 

 phenylhvdrazine reagent. The ethereal solution of chloro- 

 phyll, on standing for some days, yielded a product which 

 no longer showed the formaldehyde reaction. Form- 

 aldehvde was absent also in a sample of chlorophyll pre- 

 pared' from grass on a foggy morning. By exposing films 

 of such aldehyde-free chlorophyll to sunlight in the presence 

 of moist carbon dioxide, the formaldehyde reaction re- 

 appeared. Even in the absence of carbon dioxide slight 

 traces could be detected after exposure to sunlight ; in this 

 case the carbon dioxide is apparently formed by photo- 

 chemical decomposition of some constituent of chlorophyll. 

 In the dark, formaldehyde was never generated. The 

 results indicate that formaldehyde, as it is formed in plants, 

 enters into somewhat stable combination with a constituent 

 of the chlorophyll. Such a methylene derivative will, in 

 the presence of water, undergo only slight hydrolysis, and 

 equilibrium will be maintained in the presence of only a 

 very small amount of free formaldehyde. As this is re- 

 moved from the sphere of action by polymerisation or 

 otherwise, the chlorophyll methylene derivative will under- 

 go further hvdrolysis, with the scission of further small 

 amount of a'ldehvde. In this way the amount of free 

 formaldehyde pres'ent at any moment in the plant can be 

 regulated, and thus the highly toxic aldehyde will never 

 be present in such quantities as to harm the plant. 



Faraday Society, January iS.— Dr. F. Mnllwo Perkin, . 

 treasurer, in the chair.— S. Field : The conditions which 

 determine the composition of electro-deposited alloys. Con- 

 tinuing the study of the quantitative composition of electro- 

 deposited alloys, those of copper and silver have been 

 examined. For the electrolyte, a mixture of the double 

 cvanides was again used. Ordinarily, silver is more nega- 

 tive than copper, but the difference in their character is 

 such as would not seem to indicate any difficulty in de- 

 positing them simultaneouslv from a cyanide solution. The 

 composition of the deposits' was obtained by dissolving in 

 nitric acid, and estimating the silver as chloride, except 

 where the copper was obviously small, when_ that metal 

 was determined. When a copper coulometer is in circuit 

 the ratio (R) of the weights of alloy and copper deposited 

 in the coulometer gives a figure from which, under ideal 

 conditions, the composition of the alloy may be determined 

 thus ; — 



Percentage of silver =-^-(R - 2). 



E.xperiments soon proved that simultaneous deposition only 

 occurs within very narrow limits. Thus when the metals 

 in the solution are in the proportion of even i equivalent 

 silver to 34 equivalents of copper no deposition of copper 

 occurs under ordinary conditions of current density, but 

 when in the proportion of i equivalent silver to 100 

 equivr"-,it copper, simultaneous deposition proceeds more 

 readil '^. P. Burt : The compressibilities of helium and 

 neon.' The compressibilities of the two gases were 

 measured between the pressure limits of 850 and 150 mm. 

 of mercury. With the object of determining the lie of the 

 isothermais over this pressure range as accurately as 

 possible, a large number of volume and corresponding 

 pressure readings were made. On plotting ^v against ^, a 

 straight line was obtained in the case of both gases. 

 Helium was found to obey Boyle's law, the value of ^v 

 being independent of the pressure. In the case of neon, pv 

 diminished as the pressure diminished, and the value of 

 d{f>v)'dp.i'pv was found to be 000105.— Dr. A. C. 



