oi'O Mr. N4.PIER on Sandstones iised fur Building. 



particles where there is a paucity of lime, and may be less or more dele- 

 terious, from the source of the clay and the position of the stone in the 

 strata, that is, whether the clay has infiltrated into the stone from water 

 passing from the surface, or whether from the felspar in the fine debris 

 of granite decomposing, leaving alumina or clay, which is an ordinary 

 occurrence. As to the position of the stone in the seam the density 

 increases as we go down. A cubic inch 2 feet down weighed 19|- 

 drachms, and a cubic inch 8 feet down weighed 22 drachms. The only 

 remedy against decay I am aware being occ^ionally tried is to saturate 

 the surface of the stone with boiled oil. When care is taken to have 

 the stone thoroughly dry previous to adding the oil, this remedy has 

 been very successful, but it is not the most convenient. If the cause 

 of the decay be found to be a paucity of lime and too much clay, then 

 a simple remedy may be found in drying the stone, which could easily 

 be done by means of heat, and then saturating it with the milk of lime, 

 by which means the surface to a considerable depth would be protected, 

 and the appearance of the stone improved. When a bad stone is placed 

 in ruble work, where it is surrounded by a layer of lime, it will be 

 observed that for about one inch round the stone where the lime has 

 penetrated it there is no corrosion, and the stone compact, and lighter 

 in colour. There are some stones that are found to efiloresce in dry 

 weather, and become damp in moist weather, which is no doubt caused 

 by chemical decomposition of some ingredient in the stone; but this is 

 not the characteristic of the decay I am referring to, which is a mere 

 mouldering down, or loosening of the sand particles. The efilorescenee 

 of stone is distinct, and may be caused by the presence of sulphuret 

 of iron, which will have that effect, and which I intend to consider on 

 some other occasion on damp walls. 



In these experiments there is one thing worthy of remark, namely, 

 the great quantity of water which the stone contains. It is said to 

 require years before a house is properly dry, but it will be seen that 

 this will depend much upon the quality of the stone ; but even under 

 the best circumstances when it is considered that every cubic foot 

 of the stone contains at least one gallon water, it will give some idea 

 of the enormous quantity that has to be evaporated before a house be 

 thoroughly dry, but it is also seen that to be thoroughly dry is almost 

 impossible, as the stones absorb water from the atmosphere, more 

 especially if the stone has much clay in its composition. But inde- 

 pendent of this absorption from the air, there is also a great 

 quantity taken up by capillary attraction, more indeed than by plunging 

 it into water ; taking a cubic foot of stone perfectly dry, it will absorb 

 about one-sixth part more by placing one part in water and allowing it 

 to rise by capillary attraction, than to plunge it overhead in water, the 

 air in the latter case not easily escaping. The presence of clay in the 

 stone makes this attraction more rapid, but does not increase the 

 quantity that a stone will absorb, as the following table will illustrate : — 



