Document 91vrJ8km4dB1B2xvdwLyn9M2q

COPY March 10, 1925. Dear Mr. Yant: Enclosed is blue print of settling curves on PbBr2 fume and ZnO fume, both of which I think will interest you. The "apparent foot candles" as ordinates refer to readings on Tolman and Vliet's Tyndallmeter (JAGS 1919, page 297) while the concentrations and abscissae are .self-explanatory. Tolman and Vliet found a linear relation between illumination intensity and concentration'when dispersion was good and the line curved when it was not--an effect due to flocculation and to part icles getting in each other's way. This we find with Madox and also with burned Zn--both give pronounced flocculation. Your Pb(Et)4 experiments you recently reported were done with high rates of ventilation. Ours are intended to apply to still air only. We get some air motion in sampling with the precipitator (10 litres per min.') and some from sampling with the Tyndall meter. In the latter case the air used is returned to the cabinet bxxt the escape from the precipitator passes di rect to the room air and the air withdrawn from the cabinet is replaced through a mask impenetrable to the fume particles. The cabinet volume is about 75000 liters so this effect is probably unimportant. The PbBra fume is especially nice to work with because of the remarkable dispersion you get from the very start. It pas ses through any but excellent filters (masks) and has very little tendency to increase the resistance of the mask by plugging. You found a high percentage of the inhaled particles were exhaled and I think this is probably why. However, I honestly feel your position is not strong until you show a good deal more of the same thing. I think the betting is distinctly on your side but I cannot see you have proved anything but that powerful ventilation makes the lead hazard fromethyl gas neg ligible or perhaps nil. You have not shown that it does not exist in poorly ventilated garages. To say that 00 effects would precede the load effect does not answer this because Pb is cumulative and you considered the Pb fume as a gas in your ventilation and then determined it as made up of particles. Also t think you ought to give something about the size of the particles and their dispersion both of which are very import ant in the qxxestion of the amount retained in breathing. Your breathing experiments were fine and vie have copied the experiment in ourown work. i .' I will send you gome slides 'of PbBr2 fume if you wish. Sincerely yours. igned ) Philip Drinker