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Pyrex glass formula patent No. 1,304,623 - Page 1
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1,304,623. Specification of Letters Patent. Patented May 27, 1919.
Original application filed June 24, 1915, Serial No. 36,136. Divided and this application filed September 18, 1916. Serial No. 120,758.
To all whom it may concern:
    Be it known that we, EUGENE C. SULLIVAN and WILLIAM C. TAYLOR, both citizens of the United States of America, and residents of Corning, New York, have invented certain new and useful Improvements in Glasses, of which the following is a specification.
    In our prior application filed June 24, 1915, Sr. No. 36,136, we showed, described and claimed a glass baking dish and compositions for a glass suitable for fabrication into such dishes. The United States Patent Office has required a division of such application between the claims on the article and those on the composition and accordingly the present application is filed. Glass compositions A, B1, C, D and E given herein are compositions given in the prior application. Composition B2 given herein is specified because it is a composition which has been put into extensive commercial use and because its physical properties have been carefully and accurately determined.
    Our invention has for its object to provide a new glass (that is to say a substance containing silica in combination with various bases and acids) especially adapted for fabrication into pressed or blown ware intended for culinary or laboratory uses. For these purposes it is desirable that the glass have the following properties.
    (A) A high co-efficient of thermal endurance, as hereinafter defined.
    (B) High stability, that is to say, power to resist chemical attack.
    It is well known that certain glass making materials tend, when incorporated in the glass, to produce one or more of the desirable results, but in so doing, many of them also work against other desirable results, and in advance of an actual test, it cannot be predicted how a variation of the relative proportions of the different ingredients will affect the named factors. This invention therefore consists in the selection of certain known glass making materials in such relative proportions as will result in a glass having the named properties combined in such manner as to adapt such glass for the purpose stated and in a glass having certain desired properties.
    Generally speaking, the present invention contemplates a glass for the purposes stated, characterized by one or more of the following features,--
    (1) It is a boro-silicate of high stability having a linear co-efficient of expansion less than .000004 and a high thermal conductivity (i.e. as high as .0028).
    (2) In it the molecular ratio of silica to base is greater than 13 to 1, (tending to high stability (resistance to attack of reagents) and low expansivity), while at the same time its hardness (as measured in the manner hereinafter stated) is less than 900°.
    (3) In it the molecular ratio of acid oxid or oxids to basic oxid or oxids is not less than 15 to 1.
    (4) It has a stability better than .002 grams per 100 sq. cm. when measured in the manner hereinafter stated.
    It more specifically comprises a boro-silicate glass, in which no oxids of the second group of the periodic system are present in quantities sufficient to make them material constituents, containing over 75 per cent. of silica, and having a hardness of about 800° C.
    As examples of glass compositions falling within our invention, we give the following,--
A. B1. B2. C. D. E.
SiO2 70 80.6 80.9 90 85.0 90
B2O3 20 13.0 12.9 6 12.5 5
Na2O 4 4.4 4.4 3 1.5 ---
Al2O3 6 2.0 1.8 1 --- 2
Sb2O3 --- --- --- --- 1 ---
Li2O --- --- --- --- --- 3
Total 100 100 100 100 100 100
    All of the glasses given above have the following physical characteristics,--
    (1) A linear thermal expansivity less than .000004, between 20° C. and 300° C., the co-efficient of expansion of glass (A) being .0000037; of B, .0000034; of B2, .0000033; of C., .0000023, and of D, .0000022.
    (2) A relatively high co-efficient of true internal heat conductively, viz., .0028 calories per second per degree C. for each square centimeter of plate 1 cm. thick, for glasses A, B, and B2, and about .0030 for C.