Page:Popular Science Monthly Volume 44.djvu/439

Rh fields of bananas and pineapples dotted with orange and mango orchards, which stretch for miles beside the sugar plantations, are nearly all Chinese. They ship fruit to the southern colonies, but their profits must be very small, for one of the principal complaints made against them is that they can make a living where a white man would starve. Nevertheless, it is found that when they hire themselves out to work they are not a very great deal cheaper than white men.

Worlds and Molecules.—In his lectures at Geneva and Lausanne, M. Raoul Pictet presented mechanics as an exact science, comprising chemistry and physics in its domain. The principal phenomenon of physics is astronomy. The laws of sidereal gravitation apply likewise to the smallest bodies on the earth, to infinitely small ones like the molecules, and also to the atoms. Thus we have a unity of matter in which atoms, uniting from molecules, these group themselves into bodies, and these form worlds. The attraction which controls infinitely large bodies may therefore be regarded as similar to that which unites infinitely little ones. If the atoms touched in a molecule, there would be no force capable of separating them. We are, however, acquainted with dilatation and various ways of separating the atoms and augmenting the distance between them. The hypothesis that they touch is, therefore, not admissible. To explain the theory of chemical phenomena, let us suppose a molecule, A, placed somewhere in sidereal space, having a rectilineal motion toward another molecule, B, immovable, and very remote. In its approach to B there will come a moment when A's motion will slacken. Then astronomical phenomena will end and the phenomena special to physics will begin. At last the molecule A will stop; it has become inert, and can not advance further toward B. It is bound by cohesion. If, now, we suppose a pressure to be imposed on A, to bring it down to B, physical phenomena will cease, the resistance of A will diminish with the distance, and finally the molecule will ally itself with B without touching it; then we have chemical phenomena. The force that unites A and B is affinity. M. Pictet supposes that the absolute zero of temperature, when bodies can no longer react upon one another, is found between these last two phases, and his idea is confirmed by experiment. When sulphuric acid with potash is cooled down to $$-$$150º C. ($$-$$236º Fahr.), no reaction is apparent. The bodies are no longer able to combine at that temperature, when occurs a complete death of such action. At $$-$$80º C. ($$-$$112º Fahr.), potassium remains unattacked in alcohol and water for whole days. A slight warming produces a small reaction; and if the temperature is raised a little more, combination takes place with energy and an explosion is produced.

Heating and Ventilation of Electric-lighted Buildings.—In his paper on the Heating of Large Buildings, A. R. Wolff, consulting engineer, shows that the introduction of electric lighting with isolated generating plants in large buildings has had a sensible effect on the solution of the heating and ventilating problem by practically conditioning the use of exhaust steam for heating. The quantity of steam required for heating such buildings is nearly equal to the amount used independently for their electric lighting. Since electric-light engines convert only about ten or fifteen per cent of the heat of the steam with which they are supplied into mechanical energy, from eighty-five to ninety per cent of it is retained in the exhaust steam, available and just sufficient, as a rule, to meet the heating and ventilating needs of the building. This means practically that a boiler capacity ample for the heating and ventilating will take care, in addition, of the electric lighting of a large building, or vice versa; and that in the winter months the electric lighting is secured at only a slightly increased fuel expense. It is this fact that makes it difficult for either city or district heating or electric-lighting companies to supply steam or electricity respectively to large buildings. They can not compete with the cheapness of generation of the isolated plant within the building. The facts that electric lights give out less heat and vitiate the atmosphere less than gas, and that they do not flicker, have also an important bearing on the problem of heating and ventilation. The fresh-air supply can be brought in at the top of the room, where there are no lights for it to blow out, and