656 



SCIENCE 



[N. S. Vol. LIV. No. 1409. 



in suspension in water may be coalesced by 

 salt or lime solutions but the change is not 

 sufficient to overcome the colloidal state as in 

 the case of the coalescence of the fog particles 

 into liquid water, and on removing the coagu- 

 lating agency the colloidal matter may again 

 be put in suspension. 



As before stated the only means yet discov- 

 ered to change the colloidal nature of the soil 

 colloids is through an enormous expenditure of 

 energy in heating the material to 900° or 1000° 

 to completely drive ofE the water of hydration 

 and leave the material an amorphous mass lack- 

 ing entirely colloidal properties. This is too 

 expensive a method to be used in agriculture 

 or in road construction to particularly affect 

 the plasticity of the wet clays. The problem 

 before the soil chemist and the road engineer 

 is to bring about a change in the internal 

 energy of the soil colloid so as to break up the 

 complex hydrates and permit the atoms or 

 molecules of silicon, aluminum, and iron to 

 form a crystalline or an amorphous solid and 

 thus make the extremely plastic clays less 

 plastic and more friable. 



The molecular weights of colloids determined 

 from diffusion or from freezing point are very 

 high, reaching the figure 25,000 for starch. 

 The question arises as to whether this figure is 

 applicable to the molecule of the anhydrous 

 colloid or to the colloidal molecule associated 

 with the extremely complex system of hydrates 

 that have attached themselves to the molecule 

 of the colloidal substance. Numerous cases 

 have been reported where zeolites have formed 

 after the percolation of soil moisture through 

 exceedingly small openings in rocks and build- 

 ing stones. The question arises as to whether 

 sufficient force can be exerted to force a col- 

 loidal solution through openings too small to 

 carry the associated water of hydration, and 

 whether under these conditions, like the stir- 

 ring of a supersaturated solution, the mole- 

 cules of the colloid could be brought suffi- 

 ciently close to combine into a crystalline or 

 amorphous solid. 



This is of theoretical interest only. The 

 practical problem seems to be to find some 

 cheap method of breaking up the complex 



hydrates to give the atoms of silicon, alumi- 

 num and iron, or the hydrated molecules of the 

 silicate an opportunity to combine in a solid 

 form. 



Milton Whitney 

 BuKEAu OF Soils, 

 Depaktment op Ageicultuse 



WHEN WILL THE TEACHING OF CHEM- 

 ISTRY BECOME A SCIENCE?! 



When will the teaching of chemistry be- 

 come a science? Before answering this ques- 

 tion, let us ask another question. Wlien did 

 chemistry become a science? Chemistry be- 

 came a science when men found that there 

 were different elements; that these elements 

 had different properties; that they could be 

 changed into different forms; that they 

 would react with one another and give differ- 

 ent products and that in all these inter- 

 actions and transformations there was no 

 loss or gain of mass. These are a few of the 

 fundamental conceptions that were necessary 

 before chemistry could become a science. 



The teaching of chemistry will become a 

 science when we as teachers recognize that 

 every student is possessed with certain origi- 

 nal tendencies with which we are to work 

 just as the chemist works with the elements. 

 These original tendencies are subject to trans- 

 formations and interactions, but they can 

 not be destroyed any more than an element. 

 The law of the conservation of mass holds. 

 Sometimes the jwychologist speaks of an origi- 

 nal tendency being eliminated. He means 

 by this that the tendency has been so modi- 

 fied that you can not recognize it. The 

 chemist would say that it had suffered a 

 chemical change or had been changed into 

 an allotropic form. 



For the benefit of those people who studied 

 psychology some years ago, I might say that 

 a few of these original tendencies are curios- 

 ity, manipulation, mastery, fear, sex instinct, 

 hoarding, ownership, etc. These are the 

 rocks upon which we build our chemical 



1 Bead before the Section of Chemical Education, 

 American Chemical Society. New York, September 

 8, 1921. 



