1876.] i-JO [Britton. 



high up on the upright to allow it to be conveniently grasped when the in- 

 strument is being adjusted for use. The eye must at that time be raised to 

 a level with tlie point of the scale to watch the fluid fall gradually to ex- 

 actly that point. Should the screw be more than about thirty-four inches be- 

 low, the hand could not reach it to make the adjustment, its position must 

 therefore depend upon that of the point or length of the instrument. 



A short burette should have its thumb-screw placed at or near the bottom 

 of the stand (as shown by Figs. 1 and 3 in the plate) to afford a solid rest for 

 the hand while operating; such a rest will prevent any nervous trembling 

 of the thumb and finger when cautiously shutting off the finishing drop. 



When it becomes necessary to use a strong acid or caustic alkali, and the 

 analytical work is to be done with great accuracy, I believe that these bu- 

 rettes will give full satisfaction. There is no metal or organic substance 

 about them with which the fluid can be affected — nothing but glass. Leaking 

 to any annoying degree does not occur when the rod is not too light and 

 care is taken to exclude from the tube any granular or solid matter that 

 would prevent the rod from shutting down close; the joint must of course 

 be properly ground, and the opening not too large; but should leaking occur 

 regrinding may be done in two or three minutes by dropping into the tube 

 a few grains of emery flour with some water, and then turning the rod 

 sharply round and round, alternately lifting and pressing it a little. It is 

 best, however, not to neglect to make a note of the reading for any length 

 of time after it can be done correctly. Tlie long instrument will be found 

 very serviceable in a laboratory where many consecutive determinations are 

 to be frequently made, for one filling will answer for several, though it is 

 , rather cumbersome for only occasional work, and ordinarily the short one will 

 be preferred. They are exhibited together to illustrate the two ways of 

 placing the thumb-screw and lever. 



The third instrument (Fig. 3 in the plate) is of the kind I have had ia 

 use for about ten years, and with which a great many thousand iron deter- 

 minations have been made, always working very satisfactorily. Two of 

 them of different patterns were described in the Journal of the Franklin 

 Institute for May 1870, and in the London Chemical News for July 5th, of 

 same year. The one now exhibited has a capacity of 100 cc, with a delicate- 

 graduation, and is about forty -three inches long, the thumb-screw being 

 nearly thirty-three inches from the point of the scale, and near 

 enougli to the bottom of the stand to afford a rest for the hand. It has 

 two improvements, one of which is an adjustable piano- convex lens (E) 

 secured by movable joints to a light, metallic frame. The frame is made to 

 slide up and down easily in grooves on the sides of the upright, and has on 

 its right side a vernier. Tliis arrangement permits the scale to be read with 

 extreme precision, and when not required as in ordinary technical work, it 

 may be slid entirely off, and laid aside. The other improvement, which is 

 a minor one, consists of a single, small thumb screw (D) to hold the spring 

 valve (F) in place, while at the same time it allows the valve to be taken off 

 very conveniently when necessary to remove any matter choking the vent, 



PROC. AMER. PHILOS. SOC. XVI. 97. Y 



