﻿George.— Oji Coeds as Gas-2iroduGing Materials. 147 



the different quantities consumed during the tests. The comparisons given 

 will be slightly in favour of the gas, but not to a sufficient extent to affect 

 the value of the experiments. 



The specific gravity of the various gases I have been unable to ascertain, 

 but I am not sure that the specific gravity of gas is a reliable testimony of 

 its value as an illuminating agent, as a large specific gravity may arise from 

 the presence of carbonic acid, one of the many impurities of coal gas. 



In some instances the illuminating power is given as from twenty-one to 

 twenty-five, and an average ; in these cases the photometer was read at 

 different periods during the baking of the coal ; on the Grey coal for instance, 

 half an hour after starting the photometer gave twenty-two and a half candles ; 

 one and a half hours after starting, twenty-four candles ; two and a half hours 

 after starting, twenty candles, which was the lowest reading. 



A fact worthy of observation, and one I am unable to explain, in reference 

 to the Grey coal, is that the slack or coal dust gives a better illuminating 

 power than the large coal. 



In classifying the coals in accordance with their relative values, at the 

 head of the list I must place the New Zealand coal, from the Brunner mine on 

 the Grey River. It will be difficult, indeed, to discover any coal more suited 

 to general purposes, and for this reason I think it entitled to the first place. 

 It is not only a very good steam and house coal, but also gives a large quantity 

 of gas of very fair illuminating power. It is more free from impurities than 

 any coal I have tried, and the coke remaining after the gas is worked off is 

 large in quantity, of first-class quality, and, in burning, clinkers less than 

 the coke from any of the other coals. 



The CoUingwood coal is next best on the list, and for purely gas purposes 

 is superior to the Grey coal. The quantity and qiiality of the gas obtained is 

 equal to that from good English Cannel, but it possesses one great advantage 

 over English Cannel, viz., that it leaves a large quantity of coke of fair 

 quality. Coke obtained from Cannel is of very little value ; the CoUingwood 

 coke, however, appears to be superior to some of the coke obtained from the 

 Australian coals for heating pui-poses, but it makes a larger amount of clinker. 

 The gas obtained from this coal possesses a great advantage over most, as it 

 appears to be less affected by storage, and does not lose its illuminating power 

 so quickly. This coal contains very little sulphur, or other impurity, and is a 

 very good house coal. For steam purposes it has been tried by Mr. Kebbell, 

 of Wellington, who informs me that he finds it superior to New South Wales 

 coal, but has not yet reduced the result to figures. 



Third on the list I should place the Newcastle coal, of New South Wales. 

 Of the samples tried there is not a very marked difference, but the coal from 

 the Australian Agricultural Company's mine is, for general purposes, the best 



