490 PROCEEDINGS OF THE AMERICAN ACADEMY 



crystals, (see Plate, Fig. 6,) accompanied by very irregularly shaped, 

 but equally transparent, crystalline masses. In mixtures of equal parts 

 of molybdic acid and oxide of copper, the copper precipitate is some- 

 what inclined to gray. With sesquioxide of iron, there is a black 

 metallic-looking precipitate, not iridescent. When the iron was con- 

 siderably in excess, the precipitate was slight, and difficultly obtainable. 

 In presence of manganese, the precipitate was quite dense, and simply 

 characteristic of molybdic acid ; and such was also the case in mixtures 

 of equal parts of molybdic and tungstic, and molybdic and titanic 

 acids. 



With microcosmic salt, I have obtained a precipitate similar to, but 

 less distinct than, that noticed with borax. 



Concluding Remarks. 



Beads, at a certain point of saturation, will become wholly or par- 

 tially opaque upon cooling ; and, under such circumstances, well-defined 

 crystalline forms are sometimes produced ; but they are generally ob- 

 scured by the increase of the devitrified portion of the glass, during the 

 process of cooling. In two or three instances, however, while experi- 

 menting with baryta, I have observed distinctly marked hexagonal 

 crystals form beneath the surface of the glass (when obtained . by the 

 reheating or flaming process, the crystallizations are quite close to the 

 surface), as it cooled after complete fusion, prior to flaming, without 

 any further devitrification taking place ; and the crystals of Fig. 1 of 

 the plate are examples of this kind. 



Wherever mention is made in the foregoing pages of treatment with 

 the "reducing flame," the short, fine-pointed flame of the diagram, 

 described in the commencement, is intended, except in one or two 

 cases, where the " whole surface of the bead " is spoken of as being 

 acted on by the reducing flame ; and previous fusio7i in the oxidating- 

 fiame, and cooling of the glass, is always presupposed, unless a different 

 method of procedure is explicitly stated. An " intermittent reducing 

 flame " is also alluded to, and by this is meant repeated applications of 

 the fine jet of flame, time being allowed between each application for 

 the bead to cool. This method will often insure a precipitate where a 

 single heat would altogether fail, which is especially apt to be the case 

 in glasses not very highly charged with the subject of experiment ; for, 

 it must be borne in mind, it will not do to heat the bead too long at any 

 one time, when a precipitate by reduction is desired, as the precipitate 



