Hot extraction paper filter method

The apparatus for the hot extraction paper filter method consists of a hot extractor, a graduated receiver, a condenser, a heater and a filter paper. 

The filter paper is fitted into the cylindrical container to form a complete lining and weigh them. Then, the test portion is carefully placed and all are weighted to an accuracy of 0.05 g. Afterwards, the container is placed in the pot and sufficient solvent is poured over the sample to permit refluxing. The pot is heated to ensure a steady reflux rate of two to five drops per second from the end of the condenser. 

On completion of extraction, the mineral aggregate is removed with its container and dried to a constant mass. 

The fine mineral matter present in the solution is determined by filtering the whole solution through a suitable-grade filter paper or centrifuging it (continuous-flow centrifuge). 

The determination of the soluble binder content is carried out by difference as described in Section 9.6.1.1. 

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More information about the hot extraction paper filter method is given in CEN EN 12697-1 (2012), Annex B.1.1. 

Figure 9.4 Assembled apparatus for hot extraction paper filter method.

The hot extraction wire mesh filter method is similar to the hot extraction paper filter method. The only differences between the two methods are (a) the extraction pot (cylinder) can be made of glass or metal (b) the extraction container is a wire basket made of 63 pm wire cloth or a metal cylinder with 63 pm wire cloth sieving medium, to which the extraction thimble of the fibre material is placed and (c) a protective sieve is used. 

The duration for the extraction of the binder when the hot extraction (paper filter and wire mesh) method, a Soxhlet extractor or the centrifuge extractor method is used increases by approximately +10% of the time required for asphalts containing unmodified bitumen. 

The hot extractor is a brass or steel pot that contains a cylindrical container from non-corrodible or brass gauze of approximately 1 to 2 mm aperture size or, alternatively, a spun copper tube, with a ledge at the bottom on which a removable gauze disc rests. Two types of graduated receivers are used depending on the density of the solvent used. An assembly of the apparatus used for hot extraction by using the paper filter method is shown in Figure 9.4. 

The test is usually carried out by adding the reagent to the solution acidified with dilute hydrochloric acid carbonates, sulphites, and phosphates are not precipitated under these conditions. Concentrated hydrochloric acid or concentrated nitric acid should not be used, as a precipitate of barium chloride or of barium nitrate may form these dissolve, however, upon dilution with water. The barium sulphate precipitate may be filtered from the hot solution and fused on charcoal with sodium carbonate, when sodium sulphide will be formed. The latter may be extracted with water, and the extract filtered into a freshly prepared solution of sodium nitroprusside, when a transient, purple colouration is obtained (see under Sulphides, Section IV.6, reaction 5). An alternative method is to add a few drops of very dilute hydrochloric acid to the fused mass, and to cover the latter with lead acetate paper a black stain of lead sulphide is produced on the paper. The so-called Hepar reaction, which is less sensitive than the above two tests, consists of placing the fusion product on a silver coin and moistening with a little water a brownish-black stain of silver sulphide results. 

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