DIATOMS— CONGER 341 



They are small and light and will consequently remain suspended in 

 the air for a long time. They have a great amount of surface area 

 for absorption of the heat of adjacent burning particles. They are 

 poor conductors of heat and hence transmit it slowly to other nearby 

 particles ; in fact, they largely retain it. 



These qualities are again due wholly to the form of the diatoms. 

 Sand of the same material and size would not do, for it is too heavy 

 and would not stay suspended in the air long enough. No other 

 material can take their place in preventing dust explosions; only 

 the delicate diatom shells meet all these requirements. 



Another very different and very recent use of diatomaceous earth 

 is in the manufacture of waterproof saltcellars. Everyone is pain- 

 fully familiar with the affinity of table salt for moisture in the 

 air. In the South, at the seashore, in fact, in any locality where the 

 air becomes sultry, saltcellars rapidly clog. The advent of warm 

 weather and rising humidity exacts a toll of battered knuckles, new 

 dents in the table top, and damaged tempers, with futile efforts to 

 dislodge the salt from the top of the shaker. Attempts to overcome 

 the difficulty by putting rice in the shaker with the salt, keeping the 

 shaker under a tumbler, and other such makeshifts have long 

 proved ineffective. Whenever the thin metal cap of the usual type 

 of saltcellar, perforated with numerous openings, is exposed to the 

 moisture-laden air, there is sure to condense on it a thin film of 

 moisture to which a little salt will adliere; this salt attracts more 

 moisture, and more salt immediately sticks to the mass, rapidly 

 clogging the small openings; then corrosion may even set in, and 

 the whole thing becomes practically useless as a salt dispenser. The 

 difficulty has seemed inevitable; one of those things that "just can't 

 be helped." 



Here again the structure of the diatoms proves of unique value, 

 and only within the last year there has been placed on the market 

 an entirely new type of salt shaker involving their use, which over- 

 comes very simply and effectively the clogging difficulty (pi. 11). 

 It consists merely of a small cone of diatomite, with a single hole 

 through it, that fits in the top of the shaker under the metal screw 

 cap which serves to hold the cone in place. How then does this 

 simple device act to keep the salt dry and prevent the shaker from 

 clogging, and upon what do its unusual properties depend? Every- 

 one who has had the experience, and nearly everyone has had at some 

 time or other, of trying to wash and dry thoroughly a tall, narrow- 

 necked bottle, which cannot be wiped but can be dried only by allow- 

 ing it to drain and the remaining moisture to evaporate, realizes 

 how slowly the final moisture evaporates or diffuses out through 

 such a narrow-necked structure. Just as slowlv as it passes out 

 through such an opening, so slowly, likewise, can moisture pass in 



