1 88 TJie Vitrified Cement from an ancient fort. 



the proportions established by the prehminary trials. It is 

 already known that the presence of alkalies, especially soda, 

 increases the fusibility of a mixture, and that oxide of iron 

 acts also in the same direction. He found, however, that the 

 keystone to fusibility rested with the relative proportion of 

 alumina and its relation to the other bases. It is singular 

 that in this particular the vitrified stone agrees very nearly 

 with the proportions discovered by Seger. 



If, therefore, we take this in conjunction with the 

 peculiar composition of the vitrified stone, it would cer- 

 tainly seem to show that, in this case at any rate, the 

 materials used were an artificial mixture of natural products, 

 the proper constituents of which were arrived at by a 

 process of trial, and that the builders of the fort had some 

 acquaintance with the behaviour of different substances 

 under the action of heat, nor indeed can it be thought very 

 remarkable if they did possess some such knowledge. It 

 has been thought that in some cases the actual stones them- 

 selves were melted together by heat, and, however this may 

 be, there can be no suspicion of this in the example before 

 us. The schist, of which the fort has been built, shows 

 no marked alteration, and certainly nothing approaching 

 fusion. The temperature of fusion of such a mixture as is 

 indicated by the results of the analysis, would be about 

 1,200° C. to 1,300° C, and this could be readily attained 

 by means of wood, in the manner already suggested by 

 different writers on this subject. 



