INDUSTRIAL CHEMISTRY—BAEKELAND. 937 
Its great handicap for rapid introduction is again the question of 
freight, where heavy and expensive containers become indispensable. 
In most cases the transportation problem of chlorine is solved more 
economically by handling it as chloride of lime, which, after all, repre- 
sents chlorine or oxygen in solid form, easily transportable. 
It would seem as if the freight difficulty could easily be eliminated 
by producing the chlorine right at the spot of consumption. But this 
is not always so simple as it may appear. To begin with, the cost of 
an efficient plant for any electrolytic operation is always unusually 
high as compared to other chemical equipments. Then, also, small 
electrolytic alkali plants are not profitable to operate. Furthermore, 
the conditions for producing cheap chlorine depend on many different 
factors, which all have to coordinate advantageously; for instance, 
cheap power, cheap fuel, and cheap raw materials are essential, while, 
at the same time, a profitable outlet must be found for the caustic 
soda. 
Lately there has been a considerable reduction of the market price 
of caustic soda; all this may have for effect that the less efficient 
electrolytic processes will gradually be eliminated, although this may 
not necessarily be the case for smaller plants which do not compete 
in the open market, but consume their own output for some special — 
purpose. 
Several distinct types of electrolytic cells are now in successful use, 
but experience seems to demonstrate that the so-called diaphragm 
cells are cheapest to construct and to operate, provided, however, no 
exception be taken to the fact that the caustic soda obtained from 
diaphragm cells always contains some sodium chloride, usually vary- 
ing from 2 to 3 per cent, which it is not practical to eliminate, but 
which for almost all purposes does not interfere in the least with its 
commercial use. 
Mercury cells give a much purer caustic soda, and this may, in some 
cases, compensate for their more expensive equipment and operation. 
Moreover, there are some purposes where the initial caustic solution 
of rather high concentration, produced directly in these cells, can be 
used as it is without further treatment, thus obviating further con- 
centration and cost of fuel. 
The expenses for evaporation and elimination of salt from the raw 
caustic solutions increase to an exaggerated extent with some types 
of diaphragm cells, which produce only very weak caustic liquors. 
This is also the case with the so-called “gravity cell,” sometimes 
called the “‘bell type,” or ‘‘Aussig type,” of cell. But these gravity 
cells have the merit of dispensing with the delicate and expensive 
problem of diaphragms. On the other hand, their units are very 
small, and on this account they necessitate a rather complicated in- 
