588 
MESSRS. R. T. GLAZEBROOK AND S. SKINNER ON THE 
same time to avoid squeezing up the paste between the cork and the glass. The 
whole is now made tight by pouring marine glue over the cork, high enough to cover 
the zinc and soldering and leave only the wire projecting. The tube should rise high 
enough to receive the glue and thus secure a good adhesion. 
In the operation of pouring in the marine glue the glass is heated by the glue 
sufficiently for adhesion ; but this heat does not extend appreciably below the cork. 
Neither in this nor in any other stage of the process of charging is heat applied to 
the paste." 
Mr. Callendar’s cells were prepared in this way, except that the zinc sulphate 
solution was boiled with zinc oxide. Lord Rayleigh recommends the use of “gentle 
heat,” not boiling. The area of the zinc immersed is various in the different cells, 
being small in No. 6, large in Nos. 9 and 8. These cells have always been very close 
to the standard. They were compared with the standard No. 1 by Mr. Griffiths, 
in August, 1890. In February, 1891, they were taken to London and compared 
there with the cells in the possession of the Board of Trade. 
Cell No. 90.-—This is a large cell made in a wide-mouthed bottle, about 10 cm. 
high and 7 or 8 cm. in diameter, by one of us (S. S.) in July, 1891. The paste was 
prepared according to the Board of Trade memorandum, and is the same as that used 
in cells Nos. 71-79. (See later, p. 603.) 
The zinc was ordinary commercial plate zinc not amalgamated. At first the cell 
was too high by 25 of our units ; crystals of zinc sulphate were dropped in on July 9, 
and on July 10 it was 14 units too high. From this date onwards the tests are given 
in the Table. 
Cell No. 97.—A large cell set up by Professor Schuster, and brought by R.T.G. from 
Manchester, on July 11. The cell is set up in a kind of small Woulfe’s bottle about 
5 cm. across, and some 7 or 8 cm. high. The central opening at the top contains a 
thermometer ; the zinc and platinum pass in glass tubes through the other openings, 
being secured with sealing wax into glass tubes. There is also a mercury valve 
which permits of the escape of gas if any is evolved. 
Dr. Schuster writes as follows of the cell:—“ The cell was made with mercurous 
sulphate prepared and treated as follows :—Mercurous nitrate was prepared by 
dissolving mercury in nitric acid and boiling up the solution thus formed with mercury 
in a flat-bottomed ilask, the mercury completely covering the bottom of the flask. 
The salt was crystallised out from the solution and dried with filter paper. The 
mercurous nitrate was then dissolved in an 8 per. cent, solution of nitric acid and 
precipitated with sodium sulphate. The precipitate was filtered, washed, and strained 
by pressure, then once washed with a saturated solution of zinc sulphate. The 
sulphate was then boiled for half-an-hour in a conical flat-bottomed flask containing 
enough mercury to cover the bottom, some zinc sulphate solution and crystals being- 
added before treating ; the mercurous sulphate was then transferred directly to the 
cells, the E.M.F. directly after setting up (April 30) was — 28, the unit being 10~ 4 
