DIATOMS— CONGER 339 



There are three typical methods of heat transmission — radiation, 

 conduction, and convection. When the space within the wall is 

 filled with diatomaceoiis earth made up of the very porous little 

 shells of diatoms, any heat of radiation which might strike this 

 material is immediately reflected and radiated back into the room. 

 As there is a very small amount of contact betAveen the separate 

 shells where they touch each other, and as the silica itself is a very 

 poor conductor of heat, a minimum amount of heat will pass through 

 the wall by conduction. Most important of all, the large open air 

 space which permits of ready transfer of heat outward by convec- 

 tion currents in the uninsulated wall is now partitioned into in- 

 numerable infinitesimally minute air spaces by the little porous 

 hollow shells. Air spaces if of small dimension are the best insu- 

 lation against loss of heat, and with this type of insulation a maxi- 

 mum amount of air space is present in the wall, and yet air cur- 

 rents which might carry away heat by convection are almost en- 

 tirely prevented by these exceedingly small enclosures. 



These same principles prevent the passage of sound through a wall ; 

 or, if fine, dry diatomite powder is dusted on the surface of a newly 

 plastered wall in a church, auditorium, or theater it will adhere and 

 make a finely porous and rough, though apparently smooth, surface 

 which will stoj) the reflection and echoing of sound, thereby improv- 

 ing the acoustics. The ordinary plaster or papered wall has a hard, 

 smooth reflecting surface for the sound waves falling upon it and 

 produces echoes which interfere and reverberate. If the wall is hol- 

 low, it increases the trouble by acting as a sounding box. Hanging 

 soft draperies in front of the walls is costly, troublesome, and not 

 always desirable; they soon become dusty and are not always 

 effective in stopping echoes. The sharp edges, pores, and corners 

 of the diatom shells, however, catch the sound waves, breaking them 

 up and preventing their escape back into the room as a definite 

 interfering tone. (See pi. 12.) 



It is interesting to note that the diatom shells of powdered diatoma- 

 ceous earth will not pass through a sieve with any degi-ee of ease, 

 or scarcely even at all. We commonly think of anything small, fine, 

 and light as passing readily through a sieve, and in most of our 

 experience witli ordinary fine powders this is true; but the diatoms 

 with shells of irregular size and shape, with their horns, spines, and 

 sculptured surfaces, become all tangled up, wedged in, and locked 

 together into little fluffy balls that grow like children's snowballs, 

 picking up more and more of the shells as they roll over the surface 

 of the sieve, and defying all effort to break them up or make them 

 pass through. This characteristic of diatomite is industrially signifi- 



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