383 
ON THE DECAY OF STONE. 
(being one equivalent) of binoxide with about 44-5 per cent, (being also one equivalent) 
of protoxide; while the oxide most frequently obtained by the process above described 
contains about 65 per cent, of binoxide, which is about the proportion of binoxide that 
would be contained in a mixture or compound of three equivalents of binoxide with two 
equivalents of protoxide. The richest native oxides of manganese which chlorine manu¬ 
facturers have been in the habit of using contain about 70 per cent, of binoxide; but a 
native oxide is practically much less valuable, so far as the manufacture of chlorine is 
concerned, than an artificial oxide containing considerably less oxygen. The reason is, 
that in order to dissolve a hard, compact, anhydrous native oxide of manganese, it has 
to be digested with a large excess of acid, resulting in the production of a still-liquor 
containing a very large quantity of free acid, all of which is practically lost; whereas a 
recently formed, artificial, hydrated oxide, in an exceedingly minute state of division, 
will dissolve in a bare equivalent of acid, producing a still-liquor containing no free acid 
at all. Hence, whereas when using a 70 per cent, native oxide, it is rarely found pos¬ 
sible to obtain in the free state more than one-sixth of the chlorine contained in the 
hydrochloric acid put into the stills, an artificial oxide of less even than 60 per cent, will 
liberate fully one-third of the chlorine contained in the acid put into the stills, and this 
in far less time, and at a much less cost for labour and fuel, than the native oxide re¬ 
quires for the liberation of half the quantity. The process which I have had the honour 
to bring before the section, thus, not only substitutes the cost of about seven shillings’ 
worth of lime and three shillings’ worth of blowing for every six or seven pounds which 
the manufacturer of bleaching-powder and other chlorine products has hitherto had to 
spend upon peroxide of mangaese, but also enables him to nearly double his production 
of those products from a given quantity of hydrochloric acd. 
ON THE DECAY OF STONE; ITS CAUSE AND PREVENTION. 
BY J. SPILLER. 
For several years past I have been occupied at intervals in studying the causes of 
the decay of stone, and in experimenting with such chemical reagents as appeared to 
offer any promise of being usefully applied as means of prevention. At an early state 
of the investigation I arrived at the conclusion that the corrosive action of sulphurous 
and sulphuric acids in the atmosphere, resulting from the combustion of coal fuel, ope¬ 
rate, in large towns especially, in a very destructive manner upon dolomite and the 
numerous class of limestones commonly employed in our public buildings. This 
chemical action, aided no doubt by the simultaneous attack of carbonic acid and 
moisture, and in the winter season further supplemented by the disintegrating effects of 
frost, must, I conceive, furnish a sufficient explanation of all the facts observed. 
I would here remark that Dr. Angus Smith, Mr. Spence, and others have already di¬ 
rected attention to the immense scale of production of these sulphur acids, and have even 
quoted statistical data showing the extent or degree of pollution of the air from this 
cause in the manufacturing districts of Lancashire. When it is known that the best 
class of coal (and coke) contains usually 1 per cent, of sulphur, and that this proportion 
reaches a treble equivalent when stated in the form of the final oxidized product,—hy¬ 
drated sulphuric acid,—it follows that a ton of coal of this high quality necessarily 
evolves during its combustion nearly 70 lbs. of oil of vitriol. Here, then, is the origin 
of the sulphates which we find invariably present in the loosened crust of decayed 
stones, whether of calcareous or magnesian character. I have tested numerous samples 
of dolomite, Caen, Bath, and Portland stones fresh from the quarry, and in no instance 
found more than a trace of ready-formed sulphate ; whereas scrapings taken from the 
decayed portions of the stone of the New Palace at Westminster are bitter to the taste, 
in consequence of the comparatively large amount of sulphate of magnesia formed 
during a few years’ exposure to the sulphurous gases occurring in a metropolitan atmo¬ 
sphere. Caen stone from several buildings and localities, Portland stone, and even old 
faces of chalk cliff in the neighbourhood of Woolwich, were in like manner found to 
