12 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



product. In fact, it is rarely discovered until the cells are taken from 

 the kiln. At first, the failures from the cause alluded to were over 90 

 per cent. At the present time, about 10 per cent of the cells develop 

 cracks while in the kiln. The improvement has been due in a large 

 measure to improvements in the cutting tools and to the increased atten- 

 tion which has been given to keeping them 

 in good order. It was found impossible to 

 succeed with the usual lathe cutting tools, 

 and others with new forms of cutting edge 

 were designed. One of the more important 

 of these is shown in Figure 4. It is the tool 

 with which all the boring and nearly all the 

 inside work are done. It will be seen that 

 the tool cuts only in the longitudinal direc- 

 tion of the cylinder, bringing no pressure 

 upon the wall of the cell in a transverse 

 direction. The same principle is employed 

 in fashioning the tools with which the out- 

 side work is done. But however good the 

 design of the tool may be, failure is bound 

 to attend its use in this work unless it is 

 ground in accordance with correct princi- 

 ples, i. e., with the proper "clearance" and 

 is always maintained in a sharp condition. 



A multitude of details relating to methods 

 of mounting, speeds of cutting, etc., all of 

 which are of importance to the operator, but 

 of little interest to others, are omitted, and 

 only one instance of the many precautions 

 which it is necessary to observe will -be men- 

 tioned — the fact, namely, that, when the lathe 

 has once been started, it must not be stopped 

 until the cell is finished, owing to the danger 

 of "sagging." 



THE BURNING AND GLAZING OF THE CELLS. 



The experimental work in the baking of 

 clays was done for several years either in a FlG - 4.— Different views of special 



a i -i • i , • j. mi t001 for cutting cell (Fig. 3 B) 



feeger kiln or in an electric iurnace. Ine from cylinder (Fig. 3 4). 

 electric furnace which was first employed was 



one in which the platinum wires were woven through holes in the walls 

 and bottom of the furnace, so that the heat generated in the wires 

 must penetrate a considerable thickness of clay before reaching the 

 space to be heated. With such an arrangement a very long time 

 is required to obtain, with a given current, the temperature which 



