ASTM C25:17 pdf free download – Standard Test Methods for Chemical Analysis of Limestone, Quicklime, and Hydrated Lime.
11.5 Prnisaon and B&o—This test method was originally appnned for publication hefore the inclusion of JZeci5I(Nl and Nas statetnents within standards was mandated. The user is cautioned to verify hy the use of reference materials, if available, that the precision and bias of this test method are adequate for the contemplated use.
9. Insoluble Iattrr Including Silicon l)losidc tOptiunal Perehloric Add %lethnd
9,1 Scope—In this test method the insoluble nailer including silicon dioside is determined grasinsetrically as in the standard method except that perchloric acid is used to deitydrate the silica. The procedure is more rapid than in the standard method because only a single dehydration is necessary. Fuming perchloric acid is a very powerful dehytating agent. and silicic acid can usually be completely convened to the insoluble siLicon dioxide in less than 20 twin. This test method have been determined by tither agencies such as the Association of Official Agricultural Chemists (AOACI to be comparable to the standard hydrochloric acid method.
9.2 The fuming perchlorie acid is refluxed at this temperature for a short period of time to completely dehydrate the silica. The residue of silica and insoluble nsaner is hlten,d and washed free of acids and salts. The fIlter paper containing the residue is hurtsed off, the resultant ash is ignited at high temperature until the ash is white, and then is weighed.
9.3 Pnsedurr. Warnlng—Pcrchloric acid llClO4e is an extremely reactive liquid. When using HOD4, there are precautions to be followed which. il unheeded. may lead to .cnous explosions. Contact of the hot concentrated acid with organic matter must be absolutely avoided. Any organic matter in the sample must first he destroyed by the addition of nitric acid t11N04) to the sample prior to luitung with HOD4. All evaporations involving flUID4 must be done in a well. sentilated hood made of nonporous and inorganic material. preferably Tpe 3161 stainless steel. Facilities should be pros idesl for washdown procedures that should be performed regularly and thoroughly. These precautions on perchloric acid use are fully discussed in Practices E50
9.3.1 Weigh 0.5 g of quicklime or hydrated lime, or I g of limestone ground to pass a siese. Transfet the sample to a 2511.mL heaLer, wet carefully with a few mmllmlitres of water, and dissolve cautiously with 10 ml of concentrated nitric acid. Add 20 ml of perchioric acid and boil until dense white futnes appear. If the solution darkens at this point, add several nt,llmlitres of FINO1 until the solution clears.