INFINITESIMAL QUANTITIES RAMSAY, 229 



niton. The platinum becomes deep black and thus entirely loses its 

 transparency; and it is impossible after a few minutes to see any 

 light through the platinized plates. But before the attack began 

 a few observations were made indicatmg as the refraction {p. — 1) of 

 niton a figure approximating 0.001633 for white light, or about 45 

 times that of helium, 0.000035. You Avill perhaps remember that 

 ^Ir. Cuthbertson pointed out a very curious relationship among the 

 figures expressmg the refractions of inert elements. Those of helium, 

 neon, argon, krypton, and xenon show the simple relation 1, 2, 8, 12, and 

 20. That of niton seems to be m relationship witli the others. 



The possibility of weighing such mmimal quantities suggests in- 

 vestigations which must be very interesting. We might, for instance, 

 calculate the thickness of the layers of gas attached to solid objects, 

 for their weights are quite perceptible. Dr. Whitlaw-Gray weighed 

 a very liglit capsule of gold with a surface of about 2.5 square centi- 

 meters. After heating it to redness he at once replaced it on the 

 balance and counterpoised it. It gamed m weight for two days, 

 the total mcrease being 1,000 millionths of a milligram. Calculating 

 the thickness of such a layer of air, it appears to be seven mole- 

 cules thick. There is evidently much to be done in that respect, for 

 the substances, the nature of the gas, the temperatui'e, and the 

 pressure may be varied at pleasure. 



We have also learned another extraordmary fact. We needed 

 pure water which should leave no solid residue m evaporation. 

 Although we distilled water in vessels of platinum, silica, and silver, 

 we could never obtain a drop but there remained after evaporation 

 a crystalline deposit. We even attempted synthetic water prepared 

 by bui'nmg hydrogen in contact with chilled vessels of glass, silica, 

 platmum, and silver. The drops obtamed all left a similar deposit 

 weighing about 100 millionths the drop. We spent a weary fortnight 

 in attempts of this kind, and finally discovered that no residue is 

 obtained when water is evaporated m a current of au' filtered through 

 cotton wool. The residue came from the dust suspended m the air. 

 According to then- appearance the crystals consisted for the most 

 part of common salt, carbonate of lime, and sulphate of lime. 



Thus it is evident that water in evaporatmg is charged with elec- 

 tricity and attracts dust, which possesses a relatively great weight. 



Gentlemen, these arc some ol the experiments we have been carrying 

 out during the last few years. Instruments such as the spectroscope, 

 the microscope, and the electroscope have been highly perfected for 

 the investigation of minimal quantities. We have often had reason 

 to regret that our means of determining the quantity of matter by its 

 weight and volume have lagged so much behind. I trust we have 

 not wearied you in giving some account of our attempts to sec the 

 invisible, to touch the mtangible, and to weigh the imponderable. 

 85360°— SM 1912 16 



