54 



SCIENCE. 



[N. S. Vol. XXI. Xo. 524. 



many of the metals calls attention to a 

 possibility of error -which must not be over- 

 looked. In all eases of hydrolysis there is 

 always a possibility that equilibrium may 

 not be reached in weeks or months. The 

 only safe way is to reach the equilibrium 

 from both sides. In this way and only in 

 this way do we get any clue to the magni- 

 tude of the error involved and it is only 

 after we have done this that we are justified 

 in assuming that a reaction is irreversible. 



The application of the phase rule to the 

 fractional crystallization of rare earths 

 would certainly lead to marked improve- 

 ments. There are few people who could 

 separate potassium and sodium chlorides 

 by fractional crystallization, getting out all 

 of each salt entirely pure. Even fewer 

 would be able to separate potassium sul- 

 phate and copper sulphate. In spite of this 

 we start in cheerfully on the fractional 

 crystallization of an unknown number of 

 elements having unknown properties. The 

 result of all this is that we reach a point 

 where further separation is impossible and 

 yet we do not know why. - This state of 

 things is really the fault of the physical 

 chemist and not of the inorganic chemist. 

 It is not to be expected that the inorganic 

 chemist can start in off-hand and apply 

 the phase rule to the study of basic and 

 double salts or of rare earths. Before this 

 can be done the physical chemist m^lst work 

 out the methods and must be prepared to 

 give explicit working directions, possibly in 

 the form of recipes. 



It must also be clear to you that a study 

 of the conditions of existence of com- 

 pounds, atomic and molecular, is a pre- 

 requisite to any theory of valency, 



In the past, reactions in organic chem- 

 istry have been studied by physical chem- 

 ists chiefly as examples of reaction velocity. 

 There are two other fields which will re- 

 ceive more attention in the near future, 

 namely, yields and irreversible reactions. 



The question of yields is in a very bad 

 way. In Lassar-Cohn 's admirable book on 

 laboratory methods in organic chemistry 

 there is an enormous amount of valuable 

 material; but there is really very little in 

 the way of theory. Although we know 

 that a reversible reaction will run to an 

 end if the concentration of one of the re- 

 acting substances be kept practically zero, 

 surprisingly little use has been made of 

 this principle. We know that certain re- 

 actions take place better in dilute solutions 

 or at low temperatures or in certain sol- 

 vents, but in most cases we can not tell why. 

 In the pyridine method for introducing 

 acetyl or benzoyl groups the pyridine is 

 said to be effective because it is a weak 

 base; but it is much more probable that 

 it acts as a catalytic agent. "We do not 

 know how far the dehydrating action of 

 certain reagents is simply a question of 

 vapor-pressure or how^ far there is a specific 

 effect due to the particular reagent. The 

 action of sulphui'ic acid in the formation 

 of ether is something more than a dehydrat- 

 ing effect, and the same is true of the effect 

 of zinc chloride in the synthesis of ethyl 

 chloride. 



A single instance will be sufficient to 

 show the state of confusion that exists. 

 Anschiitz's method of preparing certain 

 esters was to saturate the solution with 

 hydrochloric acid gas and to allow the solu- 

 tion to stand overnight. Fischer improved 

 on this by adding less acid and by raising 

 the temperature. He boiled for two hours 

 and found that the hydrochloric acid con- 

 centration could be reduced to three per 

 cent, without affecting the yield. There 

 the matter is left and we are led to look 

 upon a three per cent, concentration as 

 having special merits, whereas this is un- 

 doubtedly merely a result of boiling for 

 the arbitrary period of two hours. If 

 Fischer had boiled for one hour only he 

 would have had to use a stronger acid to 



