CHEMISTRY — BAXTIDR. 183 



only progress has been in improving the methods of attack. If no new 

 difficulties arise, another year should bring definite results. Further experi- 

 ments have been made on the tensile strength of aluminum-zinc castings. 

 The results with the zinc-rich alloys are so discordant that it has been neces- 

 sary to make a special study of the casting of pure zinc. This work is now 

 under way. Owing to conditions beyond the control of Dr. Bancroft no 

 further work has been done on the constitution of the miscellaneous zinc 

 alloys. 



Baxter, Gregory P., Harvard University, Cambridge, Massachusetts. Grant 

 No. 451. Researches upon atomic iveights. (For previous reports see 

 Year Book No. 3, p. 105 ; Year Book No. 4, pp. 149, 150, and Year Book 

 No. 5, pp. 147-149.) $1,000. 



The following investigations were carried on under Professor Baxter's 

 direction : 



The analysis of iodine pentoxide, begun last year with the assistance of 

 Mr. George S. Tilley, was continued. Iodic acid, made by the action of 

 pure fuming nitric acid upon the purest iodine in quartz vessels, was purified 

 by crystallization in quartz vessels. Portions of about 10 grams of the acid 

 were carefully dehydrated in a platinum boat in a current of dry air, the 

 temperature finally reaching 240° C, and the resulting iodine pentoxide was 

 weighed. Then it was dissolved in water, reduced in dilute nitric acid 

 solution by means of hydrazine, and finally it was precipitated in thirtieth 

 normal solution with a nitric acid solution of a weighed amount of silver, 

 about 0.2 milligram in excess of the necessary quantity being used. This 

 excess of silver was determined gravimetrically after evaporation of the 

 entire filtrate to small volume. It was found impossible to use sulphurous 

 acid as the reducing agent, owing to the occlusion of silver sulphate. 



The ratio of silver to iodine pentoxide was found in 7 experiments to be 

 0.646221, 0.646210, 0.646218, 0.646194, 0.646227, 0.646209, 0.646204; aver- 

 age 0.646212. Assuming the iodine pentoxide to have been pure and using 

 the ratio of silver to iodine already determined by Baxter, 0.848843, the 

 atomic weight of silver referred to oxygen 16.000 is calculated to be 107.837, 

 which is undoubtedly a minimum value. However, the iodine pentoxide was 

 found to contain 0.0023 pcr cent of moisture. If this correction is applied, 

 the atomic weight of silver becomes 107.847. This result is lower than was 

 to be expected and the problem is being further investigated. 



Dr. Edward Mueller continued the investigation upon silver chromate 

 commenced last year by Dr. M. A. Hines. Silver chromate was precipitated 

 by the addition of a dilute solution of silver nitrate to a dilute neutral solu- 

 tion of either potassium or ammonium chromate. After being heated for 

 some time at 225° C., weighed portions of this sajt were dissolved in nitric 

 acid, reduced with either sulphurous acid or hydrazine sulphate, and the 

 silver was precipitated with either hydrochloric or hydrobromic acid. Then 



