202 



BUILDING MATEKIALS. 



was appointed, some of the stone was rejected 

 by the builders themselves. The sub-commit- 

 tee, consisting of the three chemists already 

 named, make a division of building stones into 

 2 classes: 1, those of materials not easily acted 

 on by acids ; as granites, porphyries, and ser- 

 pentines; 2, those of materials partially or 

 entirely subject to ready action of acids, among 

 which limestones, dolomites, and certain sand- 

 stones containing carbonate of lime as cement- 

 ing material, must be classed. Among analyses 

 of several varieties of dolomite, quoted in illus- 

 tration of the composition of the stone in ques- 

 tion, that of the North Anston quarry gave : 

 carbonate of lime, 54.89 per cent. ; carbonate 

 of magnesia, 42.07; protoxide of iron, 0.49; 

 peroxide of iron, 0.24 ; protoxide of manganese, 

 a, trace; silica, 0.56; water, 0.51. Not mere- 

 ly chemical composition, however, but physical 

 condition also, goes to determine actual dura- 

 bility ; thus, marble, a crystalline carbonate of 

 lime, is much less subject to influence of acids 

 than chalk, an amorphous one. Now, in the 

 dolomitic limestone of the new houses of Par- 

 liament, while the same block of small dimen- 

 sions is often greatly disintegrated in one part, 

 and wholly untouched in another, analysis 

 fails to show a difference in the chemical na- 

 ture of the two parts ; so that the cause must 

 really exist in the state of aggregation of the 

 material. Among the agents in the atmosphere 

 that may attack building stones, are: 1. Oxygen, 

 but only in case of those rare sorts containing 

 sulphurets of iron, or the protoxides of iron and 

 manganese, all of which are liable to oxidation. 



2. Carbonic, acid and water : carbonic acid in 

 presence of water proves a powerful solvent, 

 decomposing in time the most indestructible 

 rocks. The acid transforms the insoluble 

 earthy carbonates of lime and magnesia in the 

 stones containing these into soluble bicarbo- 

 nates ; the water first serving as vehicle to in- 

 troduce the acid, and then as solvent to wash 

 away the products of its action. The removal 

 in like manner of the alkaline bases from sili- 

 cious rocks, leaves the silica in more or less 

 friable condition. Besides, the committee 

 think that water exerts a gradual disintegrat- 

 ing action near to the surface of stones, by the 

 expansion occurring in its volume, upon its 

 freezing within the interstices of the material. 



3. Nitric acid : this is now known to be an al- 

 most constant, probably a normal, constituent 

 of the air ; but though it must assist in destroy- 

 ing calcareous and magnesian stones, its minute 

 quantity renders its action scarcely worthy of 

 notice. 4. Sulphur acids: these in towns, 

 especially where much coal is burned, become 

 quite appreciable. Dr. Angus Smith found in 

 the air of parts of Manchester one part sul- 

 phuric acid in 100,000, and in the centre of the 

 town, 25 parts in 100,000 of air. The com- 

 position and structure as well as the situation 

 of the stone of the new houses of Parliament 

 render it subject to action of all the agents 

 now named, save oxygen. The chief agents in 



the decay are doubtless carbonic and sulphuric 

 acids, with water ; the action of the last named 

 acid being indicated even by a marked efflo- 

 rescence of sulphate of magnesia on the face of 

 many stones from which exfoliation is taking 

 place, while its effects will be not only due to 

 solution of the lime and magnesia of the stone, 

 but also to the forming of crystals of sulphate 

 of magnesia within the pores, and which like 

 those of ice will act to disrupt and remove the 

 superficial parts of the material. 



" III. The best means of preserving the stone 

 from further injury.'" The sub-committee, al- 

 ready mentioned, begin their report on this 

 head by declaring that, among the many pro- 

 cesses for preservation that have been brought 

 to their notice, there is not one which they at 

 present feel justified in definitely recommend- 

 ing as a preservative, either for general or lo- 

 cal application. Having devoted 5 days ex- 

 clusively to the study practically of one pro- 

 cess, Bansome's presently to be described 

 they declare themselves unable to elaborate 

 even this sufficiently to warrant them in ex- 

 pressing a final opinion as to its merits. The 

 processes they had examined could be divided 

 generally into: 1, those for permanent, and 

 2, those for temporary protection. In both 

 these classes they summarily dismiss some of 

 the proposed methods, as applicable only to 

 stones before being placed in a building, or as 

 showing misapprehension of the real problem 

 to be solved among these being such as boil- 

 ing in a mixture of pitch or resin and oil ; cov- 

 ering with a semifluid mixture of silica and 

 sulphur, the latter not only oxidizable but 

 highly inflammable ; and even the offer to pro- 

 tect the walls galvanically by coating with sul- 

 phate of lead, and putting this in connection 

 with plates of zinc ; and again, to check the 

 decay by first producing fermentation over the 

 surface, in a coating of some organic and fer- 

 mentable substance. The more probably ap- 

 plicable of the permanent processes, they clas- 

 sify under 5 heads, namely : the application, 

 1, of silicates of the alkalies, in various degrees 

 of concentration ; 2, of silicates, in conjunction 

 with various saline compounds, intended to 

 produce double decomposition; 3, of hydro- 

 fluoric, or hydrofluo-silicic acid, or their saline 

 compounds ; 4, of phosphoric acid, and acid 

 phosphates ; 5, of solutions of the alkaline 

 earths, or their bicarbonates, in water. As 

 to these, however, they advise nothing further 

 than to apply, to portions of the palace wall 

 actually decaying, the best representatives of 

 the three classes last named, as an experimental 

 test of their value, deeming that experiments 

 already in progress with some of those in the 

 first two subdivisions will, in the course of a 

 few years, determine the question of their ap- 

 plicability. Of processes for temporary pro- 

 tection they recommend for trial on some af- 

 fected parts- of the wall only the solutions in 

 volatile solvents of some of the most unchange- 

 able of organic bodies, as paraffine, beeswax, 



