390 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE 



I. Chemistry axd Physics. 



1. The Single Deflection Hethod of ^yVeighing. — It is very 

 satisfactory to notice the advocacy of a simple method of ana- 

 lytical weighing by Paul H. M.-P. Brixtox, of the University 

 of Arizona, becanse several authoritative, recent text books on 

 quantitative chemical analysis recommend the very cumbersome 

 and exceedingly laborious method of very long swings of the 

 balance beam with elaborate observations, in the place of the 

 undoubtedly more accurate and far more convenient use of very 

 short swings. The method under consideration was brought to 

 the attention of its present advocate a number of years ago by 

 Dr. F. N. Guild of the same University, who had used it for 

 many years but could not give the source from which it came. 

 The present author was sceptical about it and refused even to 

 try it for 10 years, but now is strongly in its favor. 



The method of weighing is carried out by adjusting the 

 unloaded balance so that when the pans are carefully released 

 the pointer will swing out 3 divisions or more to the right to a 

 definite place. A single excursion of the pointer is the only one 

 observed. Then in weighing an object the weights are applied 

 so that the pointer makes a single excursion to the same extent. 

 Records are given of consecutive single swings, with balances 

 empty and loaded, which show that a high degree of accuracy 

 is obtainable by this method. 



The reviewer for a great many years has been in the habit of 

 observing the first excursion of the balance pointer when near 

 equilibrium in order to decide upon the proper position in which 

 to place the rider for the exact weight, but he uses finally very 

 short swings of a single division or less on each side of the 

 center of the scale. It is his experience that with rapid work a 

 slight impulse is likely to be imparted to the balance in one 

 direction or the other by the release of the pans, so that he pre- 

 fers to watch the return of the pointer from its first excursion. 

 If this excursion has been a short one of not more than two or 

 three divisions, so that the retardation of a single swing is 

 inappreciable, and the pointer returns to the exact center of the 

 scale, the indication is correct, but if the pointer does not reach 

 the center, or if it passes that point, the deficiency should be 

 added to the first swing, or the excess should be deducted from 

 it, to find the proper indication. It appears to be a usual prac- 

 tice among gold and silver assayers to adjust their very accurate 

 and delicate balances so that the zero point is indicated by a 

 definite swing, say of 2 divisions to the right and then back to 

 the center. This practice corresponds to the method under con- 



