1875.] 



195 



[Britton. 



been effected. Against hasty work, therefore, beginners should be specially 

 cautioned, and a slow discharging instrument would be best in their liands 

 I have experimented in years past, as stated at a former meeting, with 

 valves made of quite a number of substances, hard and soft. Of the hard 

 sort, glass when ground true and cushioned behind, afforded a tighter joint 

 than metal, and gave altogether the most satisfaction, but still with ordi- 

 nary every day usage would not keep in order, and withstand the pres- 

 sure of a full column of fluid without leaking more or less. Of the soft sort, 

 rubber and fine grained cork were the best; the latter proved most excel- 

 lent when solutions of potassium permangenate and bichromate were ased. 

 for, while always giving a perfectly tight joint, and being sufficiently du- 

 rable, it became absolutely inert, and neoer got sticky from ajjplications of 

 tallow like rubber. Cork has been in use at the Iron-Masters' Laboratory con- 

 stantly since 1866, and I still prefer it for my purposes; when cut perfectly 

 true and rubbed with tallow, it will make a valve from which globules no 

 larger than the head of an ordinary pin can be discharged at will. I attach 

 it to the spring with a rivet, and sometimes with a cement; for attaching 

 thin rubber I have used a cement and also a benzine solution of rubber. 

 For springs I have used platinum, brass, steel, and common tin plate. 



Of the instruments exhibited, the rod-stoppered kind have the advantage 

 of universal application, but the spring valved kind have more solidity and 

 compactness, and will bear much rougher usage. 



The one described by George A. Koenig, Ph. D (Vol. XIV, No. 93, p. 

 218, of the published proceedings) is the short, 

 graduated tube furnished by the dealers, to 

 which is fitted the thumb-screw, and spring 

 valve adjustment, the screw working through 

 the spring, and not against it. It is not perma- 

 nently movinted, and must be used like the one 

 long ago proposed by Mohr (See side view Fig. 

 5). He states that by putting a hinged joint to 

 the spring he has been enabled to use a platinum 

 valve with a 30 cc tube, the delicacy of the hinge 

 though, was found to be an objection, making 

 the valve liable to get out of order. He further 

 states that a spring coated with rubber will 

 resist the action of standard acids. The in- 

 strument is substantially what had been pro- 

 duced years before, and, as must be obvious, 

 is not so perfect as the permanently mounted one. 



