320 Scientific Intelligence. 



not be transmitted by air through a wall of dry celluloid, but it 

 passes easily if the wall is wet with a drop of water. Water can 

 be rendered very strongly active, but when kept in a sealed tube 

 it loses the greater part of its activity in a few days. When 

 kept in an open vessel the water loses its activity much more 

 rapidly, the loss being the more rapid the greater the surface 

 exposed to the air. Solutions of radium salts in open vessels 

 behave in the same way as the water just mentioned, but in this 

 case the loss of activity is not absolute, for if such a solution is 

 put into a sealed tube it gradually acquires its original activity 

 in the course of ten days or so. The authors look upon radio- 

 activity as being analogous to heat in being dissipated by radia- 

 tion and by conduction. In the latter case it passes through 

 gases and liquids, but not through solids. If a solid radio-active 

 body is left free to the air, its activity does not diminish sensi- 

 bly, and the authors have shown that a solution of a salt pro- 

 duces much more intense phenomena of induced radio-activity 

 (twenty times greater) than the solid salt itself. When the salt 

 has been in solution several days, the radio-active energy is 

 divided between the salt and the water, and if the latter be then 

 distilled off, it contains a great part of the activity, while the 

 solid salt is much less active (ten or fifteen times, for example) 

 than before solution. When left to itself the solid salt regains, 

 little by little, its original activity. The communication of the 

 activity of a radium salt to its water of solution is very slow, 

 and equilibrium is obtained only after about ten days. — Oomptes 

 jRendus, cxxxii, No. 9 ; cxxxiii, No. 5. h. l. w. , 



2. A New Method of Quantitative Analysis. — R. W. Thatchee, 

 has devised a method for determining the weights of precipitates 

 without separating them from the liquid from which they are 

 precipitated. The proposed method consists in determining the 

 weight of a measured volume of the precipitate and mother- 

 liquor, and then determining the specific gravity of the mother- 

 liquor alone. From these data, if the specific gravity of the 

 precipitate is known, the weight of the latter may be calculated 

 by the formula, 



_d{a-bd') 



X ~ d-d' ' 



where a is the total weight, b the total volume, d the specific 

 gravity of the precipitate, and d' the specific gravity of the 

 liquid. In order to apply the method, the author determined the 

 specific gravities of a number of precipitates by using known 

 quantities of soluble compounds of the substances to be deter- 

 mined, precipitating as usual in this process, and determining the 

 specific gravities of the mixture and of the mother-liquor. A 

 modification of the formula that has been given then served to 

 give the required specific gravities. The analytical operations 

 were carried out by the use of two Geissler specific gravity bot- 

 tles of 100 and 50 cc capacity. A precipitation was first made in 



