254 REPORT OF NATIONAL MUSEUM, 1899. 



sells at from $1.25 to $1.30 per hundredweight. There in apparently no difference in 

 quality between the cliffstone ground in this country and the imported paris white. 

 Its principal use is in the preparation of kalsomine. It is also employed in the 

 manufacture of rubber, oilcloth, wall papers, and fancy glazed papers. * 



Until recently all of the whiting used in this country was ground from chalk imported 

 from Hull, P^ngland. [See Specimen No. 36013, U.S.N.M.] The annual production 

 of whiting is about 300,000 barrels. The price varies, according to the quality, from 

 35 to 90 cents per hundredweight. There are four grades made, as follows: Common 

 whiting, worth from 35 to 40 cents; gilders' whiting, 60 to 65 cents; extra gilders' 

 whiting, 70 to 75 cents; American paris white, 80 to 85 cents. The uses of whiting 

 are about the same as paris white, which it closely resembles. 



The material, as should be stated, is brought mainly as ballast from England and 

 France. 



LIMESTONES; MORTARS; AND CEMENTS. Pure limestone or calcium 

 carbonate is a compound of calcium oxide and carbonic acid in the 

 proportion of 56 parts of lime (CaO) to 44 parts of the acid (CO 2 ). 

 In its crystalline form as exemplified in some of our white marbles 

 the rock is therefore but an aggregate of imperfectly outlined calcite 

 crvstals, or, otherwise expressed, is a crystalline granular aggregate of 

 calcite. In this "form the rock is white or colorless, sufficiently soft 

 to be cut with a knife, and dissolves with brisk effervescence when 

 treated with dilute hydrochloric or nitric acid. Sulphuric acid will 

 not dissolve it except in small proportions, since the exteriors of the 

 granules become converted shortly into insoluble calcium sulphate 

 (gypsum), which protects them from further attack. 



As a constituent of the earth's crust, however, absolutely pure lime- 

 stone is practically unknown, all being contaminated with more or less 

 foreign material, either in the form of chemically combined or mechan- 

 ically admixed impurities. Of the chemically combined impurities the 

 most common is magnesia (MgO), which replaces the lime (CaO) in all 

 proportions up to 21.7 per cent, when the rock becomes a dolomite. 

 This in its pure state can readily be distinguished from limestone by 

 its greater hardness and in its not effervescing when treated with cold 

 dilute acid. (See p. 274.) It dissolves with effervescence in hot acids, 

 as does limestone. As above noted, all stages of replacement exist, 

 the name magnesian or dolomitic limestone being applied to those in 

 which the magnesia exists in smaller proportions than that above 

 given (21.7 per cent). Iron in the form of protoxide (FeO) may also 

 replace a part of the lime. Of the mechanically admixed impurities 

 silica in the form of quartz sand or various more or less decomposed 

 silicate minerals, clayey and carbonaceous matter, together with iron 

 oxides, are the more abundant. These exist in all proportions, giving 

 rise to what are known as siliceous, aluminous or clayey, carbonaceous, 

 and ferruginous limestones. Phosphatic material may exist in vary- 

 ing proportions, forming gradations from phosphatic limestones to 

 true phosphates. 



Limestones are sedimentary rocks formed mainly through the depo- 



