3.--_Sulphur_ and _phosphorus_ are estimated by processes, which it would be useless to describe here. Only in case of vitriol peats is so much sulphur present, that it is recognizable by the suffocating fumes of sulphuric acid or of sulphurous acid, which escape in the burning. When peat is to be employed for iron manufacture, or under steam boilers, its phosphorus, and especially its sulphur, should be estimated, as they injure the quality of iron when their quantity exceeds a certain small amount, and have a destructive effect on grate-bars and boilers. For common uses it is unnecessary to regard these substances. 4.--The quantity of _coal_ or _coke_ yielded by peat, is determined by heating a weighed quantity of the peat to redness in an iron retort, or in a large platinum crucible, until gases cease to escape. The neck of the retort is corked, and when the vessel is cool, the coal is removed and weighed. In case a platinum crucible is employed, it should have a tight-fitting cover, and when gases cease to escape, the crucible is quickly cooled by placing it in cold water. Coal, or coke, includes of course the ash of the peat. This, being variable, should be deducted, and the _ash-free coal_ be considered in comparing fuels. 5.--The _density_ of peat-fuel may be ascertained by cutting out a block that will admit of accurate measurement, calculating its cubic contents, and comparing its weight with that of an equal bulk of water. To avoid calculation, the block may be made accurately one or several cubic inches in dimensions and weighed. The cubic inch of water at 60° F., weighs 252-1/2 grains. FOOTNOTES: [10] The apparent specific gravity here means the weight of the mass,--the air-filled cavities and pores included--as compared with an equal bulk of water. The real specific gravity of the _peat itself_ is always greater than that of water, and all kinds of peat will sink in water when they soak long enough, or are otherwise treated so that all air is removed. [11] The "full" cubic foot implies a cubic foot having no cavities or waste space, such as exist in a pile, made up of numerous blocks. If a number of peat blocks be put into a box and shaken together, the empty space between the more or less irregular blocks, may amount to 46 _per cent._ of the whole; and when closely packed, the cavities amount to 30 _per cent._, according to the observations of _Wasserzieher_. (_Dingler's Journal_, Oct., 1864, p. 118.) Some confusion exists in the statements of writers in regard to this matter, and want of attention to it, has led to grave errors in estimating the weight of fuel. [12] The _waste space_ in peat and wood as commonly piled, is probably included here in the statement, and is usually about the same in both; viz.: not far from 40 _per cent._ [13] See note on the preceding page. [14] _Der Torf, etc._, S. 43. [15] See page 00.