66 REPORT— 1870. 



Dtistfrom Grafton Street, Dublin (dried at 100° 0.). 



Inorganic matter 68'9 



Organic matter 31'1 



100-0 

 , Such dusts act as active ferments. 



Analyses of dusts taken from the principal public buildings in Dublin are given 

 in the paper, of which the subjoined is a synopsis : — 



Inorganic Organic 



matter. matter. 

 Top seats in Merrion Hall (the largest place of public 



worship) 67-9 32-1 



GaUery of the Theatre Royal 46-8 63-2 



Ancient Concerts-room (ventilating space above the 



gas) 64-3 35-7 



Nelson's Pillar (monument 184 feet high) 70-3 29-7 



The large amount of iron in some of these dusts is peculiar; for instance, that 

 obtained from the " Ancient Concerts-room " gave 21 per cent, as the amount of 

 peroxide in the inorganic matter. This probably proceeds from a slow combustion 

 of the gas-burners. 



Some further experiments were then instituted to determine how far, and to what 

 extent, these dusts would operate as ferments, and a volumetric system of measu- 

 rino- the intensity of any process of fermentation was contrived. The process is 

 based upon the reduction of a nitrate of any base to a nitrite in the presence of sub- 

 stances undergoing putrefactive fermentation. In these experiments precautionaiy 

 measures were adopted, so that all the fermentations induced were proper to the 

 dusts used as ferments. A mixture of cane- and milk-sugar was the pabulum 

 used in conjunction with mineral substances, including a weighed portion of ni- 

 trate of potassium. These expeiiments, conducted in flasks closed with cotton- 

 wool, were kept at a temperature of 20° to 28° C. They were examined from day 

 to day in the following manner : — 5 cubic centimetres of the clear liquid were with- 

 drawn with a gi'aduated pipette, and the level of the remaining liquid marked upon 

 the flask, so that it could be made up to the original level if there is any loss from 

 evaporation. The 5 cubic centimetres were then mixed with a little mucilage of 

 starch and iodide of potassium. On acidulating with sulphuric acid, blue iodide of 

 etavcli is at once formed in each case, representmg the N^ O3 present, or the nitrate 

 reduced. A volumetric solution of hyposulphite of sodium was then used for the 

 estimation of iodide of starch found. ' It is rather a curious observation that, if the 

 nitrate of potassium did not exceed J of a grain to the ounce of fermenting liquid 

 after the first 24 hours, all traces of nitrites disappear, although there is still nitrate 

 present. The results are different if we introduce 2 to 3 grains. It is probable 

 that, in the reduction of the nitrates preparatory to the assimilation of the nitrogen, 

 a nitrate is the first sta^e ; but that if the ferment bears a considerable proportion 

 to the nitrate present, the nitrogen will be assimilated in the form of some lower 

 compound of nitrogen. One point of importance is evident, that, in the examination 

 of potable waters, if nitrates are present, but if no nitrites, it is no proof that decom- 

 position is not actually proceeding at the time as regards the organic matter 

 therein. . , . 



The different results are then given in detail as regards the dust examined, and 

 which were introduced as ferments. They conclusively proved the powers of these 

 dusts for this purpose ; they also seem to point to a cm-ious phase of the subject, 

 viz. that dust taken at a great height, as from " Nelson's Pillar," seems to have as 

 gi-eat or greater activity than that which would be obtained from a building which 

 is nightly crowded to siiftbcation. This may in some measure be due to the extreme 

 levity of the spores. There is probably an altitude of the maximum of activity 

 for all localities as regards dust 



