586 
MESSRS. R. T. GLAZEBROOK AND S. SKINNER ON THE 
§ 14. Tests on various Cells used as Standards. Cells set up by Lord Rayleigh, 
Dr. Schuster, Mr. Elder, and Mr. Callendar. 
Table II. refers to cells of which most were not made by ourselves, but which have 
either been in the Laboratory for some time or have been lent us by other makers. 
In some cases comparisons of an early date made by other experimenters have been 
included. In such cases the standard used is not always quite definite, but details 
will be given. We proceed to describe the cells. 
Cell No. 1 . —This is our standard cell, made in 1883 by Lord Rayleigh, probably 
the No. 4 of his paper, ‘ Phil. Trans.,’ 1884 : “ It was prepared generally according to 
directions given by Dr. Alder Wright (‘Phil. Mag.,’ July, 1883). The saturated 
solution of zinc sulphate was nearly neutral. The metallic zinc was bought as pure 
from Messrs. Hopkin and Williams. The mercurous sulphate was from the same 
source, and the mercury was re-distilled in the laboratory.” 
Cell No. 2.— Two other cells, probably Nos. 8 and 9 of Lord Rayleigh’s jiaper, were 
left by him in Cambridge. They were set up in January, 1884. One of these has 
since dried up, the other is our Cell No. 2. The same materials as for the Cell No. 1 
were used. According to Lord Rayleigh’s tests, when first made, they were slightly 
higher—by some two or three of our units, than our Cell No. 1. 
Cells Nos. 3a, 3, 4, 5.—These are cells of the Hform suggested by Lord Rayleigh, 
made in 1886, at Wellington College, by Mr. H. M. Elder. Originally there were 
five cells ; the other has been destroyed through the bursting of the tube containing 
the zinc amalgam. They were prepared according to the descriptions given by Lord 
Rayleigh in his paper, from materials obtained from various sources, and when tested 
soon after being made, were fairly close to his standard. 
The first set of comparisons cpioted were made by Mr. E. H. Griffiths, who, at 
the same date, tested the Rayleigh cells Nos. 1 and 2. 
Cells Nos. 6, 7, 8, 9, 10, are five cells made in 1886, by Mr. H. L. Callendar, 
marked by him as I., II., III., IV., V. They are of the pattern described by Lord 
Rayleigh in his Second Paper, ‘ Phil. Trans.,’ 1885. It will be convenient to quote 
here his directions, as they will be frequently referred to. 
“ The zinc sulphate is prepared in a flask by mixing distilled water with about twice 
its weight of crystals. A little carbonate of zinc is added to neutralize the free acid, 
and the solution is effected with the aid of gentle heat. If time can be afforded, it 
is a good plan to let the solution stand, as a good deal of iron is usually deposited, 
even when ‘ pure ’ zinc sulphate is used. The solution may then be filtered in a warm 
place, into the stock-bottle. 
“ When it is intended to charge H cells, or to prepare paste, the bottle should be 
exposed to gentle warmth for a few hours, and the solution drawn with a pipette from 
near the crystals at the bottom of the bottle. Otherwise there is no security that the 
liquid used will be saturated. 
