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an eight hundredth of the vitreous materials ; and thefire was continued, in a wind furnace, from six to thirtyhours. All the glasses came out considerably coloured ;some of a deep dusky yellow ; some of a fine pale transpa-rent yellow ; some of a brown colour, greatly resem-bling that which the glass mentioned in the followingpage acquired under a muffle : some appeared yellowishor brownish when looked down upon, and of a purple-violet or reddish purple when held between the eye andthe light : some had specks and veins of a fine red ; noone was either red or purple throughout. Several of theseglasses were melted again and again, by themselves, andwith the addition of more vitreous matter : some wereworked in the flame of a lamp : some were laid in amixture of powdered charcoal and soot, and made redhot in a close crucible ; and others being laid in thesame manner, the fire was increased till they melted.The colours were by these means altered, but did not be-come uniform, or more approaching to the ruby colourthan before : some pieces, which had at first very con-siderable specks of a ruby lustre, lost them on a repetitionof the fusion.

At the same time that these experiments were tried,the same kinds of vitreous compositions, mixed with dif-ferent metallic preparations, were exposed to the fire indifferent parts of the same furnace, and were all found toreceive beautiful and uniform colours, of which an ac-count will be given in their places. To what cause themiscarriage of those with gold was owing, whether thesuccess, in regard to this metal, is influenced by the quan-tity of the matter, by the unsteadiness of the heat in asmall furnace, by the fusibility of the vitreous composi-tion, by the metallic matter being ground with the ingre-dients before their exposure to the fire or added to them

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