includes a discussion of the meaning of hydrogen-ion concentration and PH, of the methods of p~ determination, and of titratian errors. Pages 25 to 74, inclusive, deal with applications of hydrogen-ion c o n t r o l m e t h o d s i n some t h i r t y industrial and scientific fields. The re-
mainder is devoted to materials and equipment. Numerous references t o the literature are given. The professor or student of physical or industrial chemistry will find the booklet useful and suggestive. 0. R.
New Property of X-Rays Discovered. While the biologists attending the meeting of the American Association for the Advancement of Science were listening to accounts of newly discovered ways in which x-rays affect living tissue, the physicists heard about another new property of these rays. Dr. Fred Allison, of the Alabama Polytechnic Institute a t Auburn, Alabama, told the American Physical Society how he had found that they change the effect of certain liquids and other substances on light. Many liquids, such as a sugar solution, have the property of turning the plane of polarized light. Ordinary light consists of vibration in an indefinite number of directions, hut when polarized the vibration is confined t o one particular plane. If a beam of such light is passed through a sugar solution, i t is still vibrating in one direction when i t emerges, hut in a different direction from that when it went in. Dr. Allison has found that even liquids which do not ordinarily have this power gain i t when exposed to x-rays. When liquids, or glass, are placed in the field of a powerful magnet, they gain this property, as discovered many years ago by Faraday. When x-rays are used in addition, says Dr. Allison. the rotatory powers of the liquids are increased, while in glass it is made to rotate in the opposite direction.-Science Service Measures Electric Charge of Diphtheria Germs. The ability of a living diphtheria bacterium t o pour poisons into the blood stream of humans bears a relation to the size of the charge of electricity which each bacterial cell carries, according t o Drs. I. S. Falk, I,. B. Jensen, and J. H. Mills of the University of Chicago. Their electrical measurements can be made in a few minutes and with simple apparatus on cultures thought t o be capable of producing toxin. The results are obfained much more rapidly than by time-consuming methods of animal experimentation. The electrical method is based on the fact that the power of the bacterium t o excrete poisons depends on the porosity of its outer wall. This, in turn, affects the electrical charge on the cell as a whole. The observation is made by placing the suspected organisms in a small chamber between metallic plates charged t o a definite electrical potential. The rate a t which the bacteria cross the electrical field is then watched through a microscope. The virulence of the germs can be calculated by reference to the rate of "migration" of a strain of diphtheria of known toxin-producing power. This new method is expected to speed up detection of cases of diphtheria, and t o facilitate release from quarantine.-Science Service
