14 THE ATOMIC WEIGHTS OF 



stricted end of the platinum combustion tube and gave rise to 

 two ground joints at (a) and (c). In the final determinations 

 this combustion tube had no particular significance. Originally 

 it was intended to vaporize the methyl alcohol from boats placed 

 in the combustion tube and to conduct the vapor through the 

 bulb. However, as this method seemed to offer no particular 

 advantages and was not easily controlled, all liquid reagents (such 

 as water, acids, methyl alcohol) were introduced through the 

 tubulature shown at (6) by means of a small platinum funnel. 



In general the ground joint at (a) was disturbed as little as 

 possible during a determination. When operations had to be 

 interrupted the apparatus was disconnected at (c) and the bulb 

 together with the elbow piece put on a suitable rack in a desic- 

 cator. Before each weighing, however, the elbow was removed; 

 the bulb could then be closed completely by the hollow platinum 

 stopper (d). The entire apparatus weighed about 56 grams. 



It may not be amiss to add, concerning the ground platinum 

 stoppers and connections, that manufacturers often use pumice 

 and oil for grinding such parts, and a platinum surface so treated, 

 of course, requires careful cleaning. In the present instance all 

 platinum parts having ground surfaces were immersed for some 

 time in molten sodium carbonate and then in molten potassium 

 bisulphate; but after this treatment the joints were found to 

 "stick" and were as useless as before. To remedy this defect 

 the stoppers and joints were carefully reground with a mixture 

 of pure, very finely powdered oxalic acid and glycerol. This 

 required considerable time, as the oxalic acid acts only as a very 

 mild abrasive. The parts thus prepared were then thoroughly 

 cleaned and ignited and finished with a little glycerol alone. Any 

 particles of oxalic acid which might have become embedded in 

 the platinum were easily decomposed upon ignition. The con- 

 nections obtained in this way proved very satisfactory. A proper 

 functioning of the joint at (a) was imperative, because it marked 

 the juncture between the container to be weighed and the rest of 

 the apparatus. A number of " make-and-break " operations at 

 this joint did not perceptibly affect the weight of the former. 



The bulb was not allowed to come in contact with a direct 

 gas flame, but was heated in an air-bath formed by a large platinum 

 crucible. For the lower temperatures the crucible was set into a 



