Koenig.] 218 [Aug. 21, 



the product of a partial, and in many instances of a pretty thorough al- 

 teration of the original corundum into micaceous and chloritic schists or 

 beds, or, as Prof. Dana would express it : " « pseudomorphism on a broad 



scale.'''' 

 University of Pennsylvania, July 4th, 1874. 



CONTRIBUTIONS FROM THE LA^BORATORY OF THE UNIVER- 

 SITY OF PENNSYLVANIA. 



NO. II. 



ON AN IMPROVEMENT OP THE BURETTE VALVE. 



By Geo. A. Koenig, Ph.D. 



(Read before the American Philosophical Society, August 21, 1874). 



Strictest simplicity of construction must be considered as the first re- 

 quirement of any tool or apparatus, besides fitness for all work within 

 its sphere of action. Frequently we meet with constructions in which 

 fitness has been sacrificed to a considerable extent for the sake of sim- 

 plicity, and quite as often the reverse. There are cases, indeed, in which 

 circumstances demand even a certain degree of one-sidedness, but in my 

 judgment a more complicated apparatus, overcoming defects of working 

 attached to a simpler device, is practically the more desirable of the two. 



"When Frederick Mohr gave his rubber tube valve to volumetric analy- 

 sis, he had indeed hit, like a true genius, upon the simplest contrivance 

 imaginable. To this piece of apparatus must be ascribed the rapid adop- 

 tion of volumetrical determinations by analytical chemistry. No matter 

 how simple the volumetrical reactions might be, if they had to be exe- 

 cuted by an unhandy manipulation, the practical chemist would rather 

 keep on with his accustomed precipitations and weighings. 



Let us consider now the conditions under which the burette will satisfy 

 all demands which can be made upon it, 



1. The instrument must not engage the hands of the operator during the 

 operation. 



This condition requires the burette to be fixed and its position to be 

 quite independent from the person of the manipulator. 



2, The instrument must allow a rapid discharge of its liquid contents to 

 any desired volume, loithout the application of another force than that of 

 gravitation. 



This condition requires the tube to be fixed vertically and to be fur- 

 nished with a valve. 



3. The valve must allow to interrupt the current instantaneously and 

 completely, and also the regulation of the liquid current from the. smallest 

 drop to a full stream. 



4, The working of the valve must be easy, not require any efort on the 



