Sentence:  The photochemical reaction cells consisted of 10 mm. i.d. <WSD>Pyrex</WSD> tubing , 5.5 cm. long , diffraction effects being minimized by the fact that the light passed through only liquid glass interfaces and not gas glass interfaces . 
Meaning of the word marked with <WSD> tags:  a borosilicate glass with a low coefficient of expansion; used for heat-resistant glassware in cooking and chemistry