MR. F. E. SMITH ON THE NORMAL WESTON CADMIUM CELL. 407 



in length. The question is an interesting one, and we hope to extend our investigation, 

 but at present there appears to be no necessity to stipulate the size of the crystals. 

 We would, however, draw attention to the uniformity of the size of the crystals of the 

 chemically precipitated salt, and as Method II. is the easiest of any of the methods of 

 preparation used by us, we strongly recommend it, or one founded on it, as a standard 

 method of preparation. 



Constancy of the. Cell. 



The results recorded in Table I. indicate remarkable constancy of most of the cells. 

 Eighty per cent, of the first fifty cells have apparently varied by not more than 

 2 parts in 100,000 since the first month of their preparation. Of the remainder, four 

 have varied from 3 to 5 parts, one 6 parts and one 16 parts in 100,000. There are 

 four others which belong to the N group of cells ; these were low at first, but rose to 

 the normal value 3 months after preparation. Further remarks on these four cells 

 appear on p. 410. The last eight cells in Table I. are anomalous. In 12 months the 

 three M cells have fallen 10, 16 and 21 parts in 100,000 respectively, and the five 

 D cells have values about 30 parts in 100,000 lower than the normal. Of the 

 approximately constant cells, twelve have been set up for 2^ years, twenty-three for 

 more than 18 months, and thirty-six for more than 12 months. It is important to 

 note that the comparatively new cells, i.e., those set up in March and April, 1907, 

 are practically identical in E.M.F. with the cells set up in 1904. 



Of the abnormal cells it is noteworthy that, with the exception of E 67, they 

 belong to three groups and that the change in them has been practically continuous 

 from the time of their construction. The cells were prepared in a manner apparently 

 the same as that of the normal cells, and we are unable to offer a complete explanation 

 of their remarkable behaviour. Examination of the solutions shows that they are not 

 appreciably acid, and tests on the amalgams indicate that they give the same E.M.F. 

 as those used in the new cells. The depolarisers are, however, at fault. This we 

 have proved by connecting one of the cells with a new cell by means of a syphon and 

 measuring the E.M.F. between the negative pole of the new cell and the positive 

 I>ole of the abnormal cell. The same low E.M.F. was recorded. Something may have 

 happened during the preparation of the depolarisers for these abnormal cells, but we 

 are not aware of any departure from our usual proceeding. 



There is, however, another indication that the depolarisers have changed, and we 

 wish to draw particular attention to this, as it may lead to the discovery of the cause of 

 the disturbance. In nearly all of the cells which have fallen by as much as 0'0002 volt 

 many of the small crystals of cadmium sulphate have changed in colour, and in some 

 cases the colour of the depolariser has also changed. The cadmium sulphate crystals 

 in these cells of low E.M.F. are of a yellowish- brown tint and the mercurous sulphate 

 in places is slightly yellow, or, in a few instances, green. This change has also been 

 noted in cells set up with some samples of purchased mercurous sulphate, but these 



