602 Professor A. H. Church [April 12, 



depth, maybe 2 or 3 inches. The baryta forms an insokible sulphate 

 with the sulphuric constituent of the gypsum and of the other 

 sulphates present, and at the same time calcium hydrate is set 

 free. This probably in part unites with soluble silica, but most 

 of it gradually becomes carbonated, while the calcium carbonate 

 thus regenerated actually reconstitutes the original binding cement 

 of the stone. This description applies especially to sandstones 

 compacted by calcium carljonate ; but limestones illustrate the same 

 changes. Unlike water-glass and most of the other preparations 

 which have been used for hardening decayed stone, baryta forms 

 no crust on the surface — indeed it produces no sensible effect on 

 the outside until it has penetrated to the deeper parts. So when the 

 Dean of Exeter, in his letter published in The Tmies of October 26 

 last year, stated that " baryta does not strengthen the stone struc- 

 turally, it forms a scab of the decayed stone on the face of the 

 sound stone, which, as is the case with all scabs, has a tendency to 

 peel off," he could hardly have selected more inappropriate terms in 

 which to describe the action of baryta. The Dean further stated his 

 belief " that the decay at Westminster was comparatively superficial.'* 

 Surely very few persons would regard a decayed layer 2 or even 3 

 inches thick as superficial. And he raises the question whether the 

 baryta- treatment, which his friend the late Mr. Micklethwaite told 

 him seems to be successful "so far as we can judge yet," would 

 answer outside a building as well as inside. Here I may cite the 

 case of Chichester bell-tower. On analysing portions of decayed 

 stone from the several faces of this campanile, I found sufficient 

 sulphate present to warrant the application of baryta-water to a 

 trial area. This was done some two or three years ago with so 

 satisfactory a result that last July Mr. Somers Clarke, the architect, 

 decided upon treating the whole of the octagon and the entire 

 north face of the tower in the same way. He wrote : " the success 

 of the experiment fully justifies this course." There is no need to 

 multiply references to other successful trials of the use of baryta in 

 strengthening external decayed stone-work and stopping further 

 damage, but in the course of the next few years it may be expected 

 that many favourable reports will be forthcoming. Experiments, 

 large and small, are being and have lately been made, and promise 

 well. I have been told of a single failure, but I learnt that the 

 architect in charge expected that the consolidation of the decayed 

 stone would be immediate, and had not waited for the few weeks 

 needed for carbonation to take place. It is proper to add that 

 where decay has resulted from simple weathering — the action 

 mainly of water and carbon dioxide — or from sea-salt, the ti'eat- 

 ment with baryta is not ai)plicable. Nor should it be forgotten 

 that baryta water is toxic and easily spoilt by exposure to the air. 

 Then, again, there may be too little gypsum present in the decayed 

 stone for an adequate liberation of caustic lime to occur. Without 



