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LYII. On some Bloivpipe Reactions. i?yE. J. Chapman, 

 Ph.D., Professor in University College, Toronto *. 



QiV the Opalescence produced by Silicates in Phosphor-salt. — 

 It is well known that most silicates when fused with 

 phosphor-salt are only partially attacked — the bases, as a rule, 

 gradually dissolving in the flux, whilst the silica remains in 

 the form of a flocculent mass technically known as a " silica 

 skeleton." Very commonly, almost invariably, indeed, if the 

 blast be long continued, the bead becomes more or less milky 

 or opalescent on cooling. This latter reaction was apparently 

 regarded by Plattner as essentially due to the presence of 

 alkaline or earthy bases, such as exhibit the reaction per se. 

 He states (Probirkunst : Dritte Auflage, p. 468) — " Da man 

 nun von mehreren Silikaten ein Glas bekommt, welches, so 

 lange es heiss ist, zwar klar erscheint, aber unter der Abkuh- 

 lung mehr oder weniger opalisirt, so muss man sich von der 

 ausgeschiedenen Kiesels'aure iiberzeugen, so lange das Glas 

 noch heiss ist, und dabei die Loupe zu Hiilfe nehmen. Die 

 so eben erwahnte Erscheinung tritt gewohnlich bei solchen 

 Silikaten ein, deren Basen Kalkerde, Talkerde, Beryllerde 

 oder Yttererde sind, die fur sich mit Phosphorsalz, bei gewis- 

 ser S'attigung des Glases, unter der Abkuhlung oder durch 

 Flattern milch weiss oder opalartig werden." Dr. Theodor 

 Eichter, the editor of the 4th edition of Plattner's work, 

 leaves out the " gewohnlich" of the above quotation, and so 

 makes the implication still stronger. In this vierte Auflage, 

 the statement runs — " Bei solchen Silikaten deren Basen fur 

 sich mit Phosphorsalz, bei gewisser Sattigung des Glases, 

 unter der Abkuhlung oder durch Flattern milchweiss oder 

 opalartig werden (Kalkerde, Talkerde, Beryllerde, oder 

 Yttererde) wird die Perle unter der Abkuhlung mehr oder 

 weniger trube." It is true enough that silicates in which 

 these bases are present, exhibit the reaction ; but as other 

 silicates, practically all, indeed, exhibit the reaction also, the 

 inference implied in the above statement is quite erroneous. 

 The opalescence of the glass arises entirely from precipitated 

 silica. If the blast be sufficiently kept up, a certain amount 

 of silica is almost always dissolved ; but this becomes precipi- 

 tated as the glass cools. A simple experiment will show that 

 this is the true cause of the opalescence. If some pure silica 

 (or a silicate of any kind) in a powdered condition, be dis- 

 solved before the blowpipe-flame in borax until the glass be 

 nearly saturated, and some phosphor-salt be then added, and 



* Communicated by the Author. 



