NA TURE 



391 



THURSDAY, FEBRUARY 3, 1910. 



niE DEVELOPMENT OF GLASS-MAKING IN 

 JENA. 



L'ie Glasindustrie in Jena. Ein Work von Schott iind 

 Ahhe. Geschildert von Eberhard Zschimmer. Mit 

 Zeichnungen von Erich Kuithan. Pp. 160. (Jena : 

 Eugen Diederichs, 1909.) 



THE history of the firm of "Otto Schott und 

 Genossen " may be said to commence from the 

 date of May 27, 1879, when Otto Schott first addressed 

 from Witten, in WestphaHa, to Ernst Abbe, pro- 

 fessor and director of the observatory in Jena, a letter 

 relating to some experiments he had recently been 

 making in the production of lithium glass. He 

 wrote : — , 



" Recently I produced a glass into which was intro- 

 duced a considerable amount of lithium, and of which 

 the specific gravity was relatively low. I anticipate 

 that this glass will show, in some direction or other, 

 exceptional optical properties, and would ask you 

 whether you are prepared to examine it as regards 

 its refractive and dispersive qualities to determine 

 whether my anticipation is correct." 



The glass had been made in a small experimental 

 furnace of Schott's design. The mixing was imper- 

 fect, and Abbe's report was to the effect that the 

 glass contained too many striae for optical determina- 

 tions to be made. It was not long before this difficulty 

 was surmounted, and vi-ith stirrers made from the 

 stems of Dutch clay pipes, Schott succeeded in pro- 

 ducing in small quantities in the laboratory experi- 

 mental meltings homogeneous enough to allow of a 

 complete determination of their optical properties. 

 This determination, however, brought a new dis- 

 appointment; for the secondary spectrum of an objec- 

 tive in which the crown glass of Fraunhofer was 

 replaced by the new lithium-crown was more pro- 

 nounced than before. The lithium glass, indeed, 

 showed exceptional properties, but they were not in 

 the direction desired. 



The work was not immediately continued. A year 

 elapsed before Abbe urged that it should be resumed. 

 Schott thought of State aid, but Abbe, more experi- 

 enced, represented the uselessness of applying for 

 help from public funds until laboratory results of 

 promise had been reached. In a letter of December, 

 18S0, he suggested the main products to be desired 

 from the point of view of technical optics. 



(i) Crown glass of appreciably lower mean disper- 

 sion than that yet known, or of higher refractive 

 index with the same dispersion. 



(2) Flint glass the relative dispersion of which in 

 passing from red to blue agrees more closely through- 

 out the spectrum with that of crown (thus giving 

 smaller secondary colour aberrations). 



(3) Flint glass of very high dispersion, but of 

 smaller mean refractive index. 



The work was re-commenced on a more comprehen- 

 sive scale. A systematic examination of glasses of 

 NO. 2IOI, VOL. 82] 



varying' composition was planned. To Schott, how- 

 ever, the procedure seemed to promise to be too pro- 

 tracted, and here his general chemical knowledge, and 

 especially his acquaintance with mineralogy, served 

 to shorten the path. Almost instinctively he fixed on 

 the addition of phosphates and borates as the sub- 

 stances most likely to give glasses of novel character. 

 As is well known, his intuition proved correct, and 

 resulted in the foundation of a new industry. On 

 October 7, 1881, Abbe, in sending greetings on the 

 one-hundredth melting, writes : — " The problem of 

 the complete achromatisation of the telescope objective 

 I regard as solved by the two meltings 78 and 93 " — 

 two borate glasses. 



The next step was the industrial realisation of the 

 results proved possible in the laboratory. For this 

 capital was needed, but in January, 1882, a " Glas- 

 technisches Laboratorium " was founded in Jena by 

 Abbe and Schott, in conjunction with Carl Zeiss and 

 Dr. Roderich Zeiss. It was just at this time that 

 Dr. Wilhelm Forster, director of the observatory and 

 of the Normalaichungskommission in Berlin, was 

 pressing that the Ministry of Finance should give 

 State aid to an industrial research to determine satis- 

 factory glass for the making of thermometers.^ In 

 February, 1S82, the Jena company became acquainted 

 with Fo'rster's aims. It was a matter of course that 

 Schott should be asked to carry out the new inves- 

 tigation. Preceded by an examination of the varieties 

 of thermometer glass then in use, Schott's new ex- 

 perimental meltings began in March, 1883, and by the 

 end of the year promised so well that on this side 

 also the question of the foundation of a new indus- 

 trial undertaking merited serious consideration.^ In 

 January, 1884, the promoters entered into new articles 

 of association, with a capital of 60,000 marks, and, 

 with the value of the work urged on them by various 

 physicists of eminence, the Prussian authorities con- 

 tributed, in the first two years, a further sum of 

 60,000 marks. 



The present work was written to celebrate the twenty- 

 fifth year of the life and development of the Jena glass 

 works. Dr. Zschimmer's volume gives a popular 

 account, not only of the circumstances which led to 

 the foundation of the world-famous works, but of the 

 technico-scientific problems which, in virtue of the 

 researches there undertaken, have one after another 

 been successfully solved. The relation of chemical 

 composition to optical properties, the questions oi 

 homogeneity, durability, freedom from mechanical 

 strain and from colour, these and all the main ques- 

 tions connected with the production of glass ior 

 scientific purposes are dealt with in a manner which 

 renders them intelligible to the ordinary reader who 

 is not specially interested in the scientific problems 

 involved. 



The processes of manufacture, the various types of 

 furnace, the fabrication of the melting-pots, the 

 methods of production of glass vessels of various 

 forms, glass tubes, &c., the machinery for the pro- 

 duction of glass bottles, the manufacture of gas- 

 mantle cylinders, and other problems rather of a 



P 



