770 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



glass under the influence of moist air. He has found this to be easily 

 measurable, and the following table is a classification (by metals, not by 

 oxides) of some important varieties. 



Applicability for 



Thermometers ; 

 chemical purposes 



Optical crown- 

 glass 



} 



Ditto | 



Optical flint-glass < 



Ditto 

 Chemical purposes 



Plate-glass 



Optical glass 



Ditto 

 Ditto 



Chemical Class 



Sodium-alurninium- 

 boro-silicate 



Ditto 



Potassiurn-barium- 

 zinc-boro-silica 



Potassium-sodium- 

 lead silicate 



Potassium-barium- 

 zinc-lead-silicate 



Sodium-calcium- 

 zinc-boro-silicate 



Sodiurn-calcium- 

 silicate 



Sodium-barium-zinc- 

 boro-silicate 



Sodium-aluminium 

 boro-silicate 



Ditto ■ 



Description 



Relative 



Decomposa- 



bility 



> Jena, No. 59iii 



Jena, No. 3917 



| Jena, No. 4556 



| Jena, No. 4113 



\ Jena, No. 4531 



1 Stutzerbach 



J " Resistance-glass " 



) " Rheinish mirror- 



) 



glass." 



Refractive Index 

 n = 1.518 



n = 1-464 

 n = 1-461 



3 

 3 

 5 



5 



5 



8 



20 



60 



600 



1800 



Ultramicroscopic Examination of Colours of Textile Fibres.* — 

 J. Schneider and J. Sourek, in continuing the investigations of Schneiden 

 and Kunzl upon the above subject, endeavoured to approach their task 

 from two points of view. 1. From the theoretical standpoint — with 

 the object of discovering whether distinctive appearances could not be 

 found with regard to regular pigment deposits in the case of direct 

 colouring of cocoon silk. 2. From the practical standpoint — with the 

 object of establishing the applicability and trustworthiness of the 

 ultramicroscope in the testing of textile fibre pigments, with the hope of 

 giving a very simple introduction to this testing. 



In the case of the first it was hoped that by the use of polarized 

 light distinctive rotations of the plane of polarization might be definitely 

 connected with certain conditions of silk-coloration. The results were, 

 however, unsatisfactory. 



In the case of the second point of view, uniformly broad strands of 

 silk from the middle part of the cocoon could be usefully examined. 

 If these furnished only small portions of an absorption spectrum it was 

 found that the colours in the two crossed-nicol positions were com- 

 plementary. Thus this method of examination might be useful when 



* Zeitschr. wiss. Mikr., xxvii. (1910) pp. 219-26. 



