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to be maintained. As a result we started heating the rooms by means of Primus
stoves to a temperature of over 65 degrees F. With this, results were better, but they
were not quite satisfactory, and by chemical analysis it was found that the concentration
of washed heavy naphtha in a room varied, being denser at lower levels. Because
of this it was necessary to provide a "reservoir" of the fluid near the ceiling and
this was done in the first instance by the use of blankets, stretched across from
the picture rails, or, if there were not any rails, by means of hooks in the walls.
This arrangement was not altogether satisfactory because it was found that on
occasion the wet blankets drew the picture rails away from the wall or pulled out the
hooks. Ultimately a lighter material—a tennis sponge—was used and this gave
much better results. With this the idea of a "reservoir" was dropped and we began
to use diffusion screens, from floor to ceiling, three inches away from all walls. About
this time a delayed action sprayer, working by clockwork was invented, and it
became possible to reinforce by mechanical means the naphtha on the screens—some
eight hours after the rooms had been closed. When these diffusion screens were
first used it was apparent on entering the room the following day that the concentration
was much stronger than before, and that there was a definite "kick" in
the atmosphere. In order to measure this "kick" an experiment was made. Three
similar rooms in three adjoining empty flats were dealt with as follows, equal
quantities of washed heavy naphtha being used in each room.
(i) In the first room the walls were sprayed in the original way;
(ii) In the second room the walls were draped and the drapings were sprayed;
(iii) In the third room the walls were draped and a delayed action sprayer,
charged with half a gallon of washed heavy naphtha, was set to go off eleven hours
afterwards.
Samples of air were taken the following morning and it was found that in the
first room the concentration was .14 percent. naphtha, in the second room .22 per
cent., and in the third room, .25 per cent. The maximum concentration which could
have been obtained at the atmospheric temperature that day was .27 percent. We
had now learned that by means of drapery we could increase the efficiency of naphtha
by nearly 60 per cent., and by using the delayed action sprayer as well, by about
80 percent. It was clear that drapery would be used in the future. It was now
necessary to find an easy means of fixing the drapery. Different ways were tried,
but ultimately Mr. Sumner, one of the Council's Sanitary Inspectors, hit on the idea
of using electric conduit tubing, using tubing of different sizes so that one piece
could be telescoped into the other. The method consists of a framework of metal
junction boxes and tubing. The tubing is cut into standard lengths—uprights of
7ft. 9 ins., corner pieces 2 ft. 3 ins. long, and connecting pieces 4 ft. and 6 ft. long.
Simple additions enable this apparatus to be used in staircases and in corridors. The
largest possible oblong is constructed in the room, and the drapery hung from it in
double lengths, i.e., 15 ft. long. A cheaper material, Egyptian cotton, is now used
for the drapings. The fitting takes about five minutes per room to erect. The
roof space is treated differently. There is much movement of air in the roof space