380 Some Account of the Monuments 
periments, M. Gehlen found that the following proportions were 
the best : } 
100 sand, 50 dry sulphate of soda, from 17 to 29 of quick-- 
lime in dry powder, and 4 of charcoal. | 
This composition always gives, without the addition of any” 
other flux, a very fine glass for drinking-glasses ; and we remark 
neither any sulphurous smell, which was sometimes so strong as - 
to overpower the workmen, nor the extraordinary crackling” 
which is manifested in the melting-pots when other proportions 
are employed. . 
After numerous observations M. Gehlen announces the follow-_ 
ing results : 
i. The sulphate of soda may be employed in the manu- 
facture of glass, without the addition of any other saline flux. 
The glass, which results is equally beautiful with that made with _ 
the usual materials, and it possesses all the properties of that” 
made with soda. » 
2. The sulphate of soda alone, is but very imperfectly vitrified” 
with the silex, even when heat is long continued. By the 
intermedium of lime, the vitrification succeeds better, but not 
in the proportion of the lime and the combustibles which must | 
be employed. 
3. The vitrification takes place, on the contrary, in a short 
time and in a perfect manner, by means of any substance which 
decomposes the sulphuric acid of the sulphate of soda, and thus 
destroys the powerful affinity which hindered the soda from 
acting on the silex. It is charcoal which best attains this ob= 
ject: nevertheless in the preparation of flint glass its place may 
be supplied by metallic lead. ¥ 
4, This decomposition of the sulphate of soda may be effected 
during the vitrification itself, or previous. Local circumstances | 
may determine, in the choice of one orother of those processes 5 
but the employment of the latter presents no difficulty what- 
eyer. ¥ 
LXXVIII. Some Account of the Monuments of Thebes in 
Egypt*. 
Orr knowledge of the monuments of Thebes was, until lately, 
so limited and imperfect, that but very little could be said on the 
subject with any certainty. Among the numerous travellers 
who have visited Egypt, some have merely penetrated into 
* Translated from the Appendix to the work published by M, Hee n, 
of the University of Gottingen, entitled Ideen iiber die Politik, den Verkehs 
und den Handel der Vornehmsten Voelker der Alien Welt. Sd Editio 
Gottingea. 1815. : 
