=2. Fouling.=--(i) Fouling is of two kinds: (_a_) _Internal_, probably caused by the forcing of gas or harmful material into the pores of the metal; (_b_) _Superficial_, caused by the deposit in the bore of the solid products of combustion of the charge and of the cap composition. The result of neglect in either case is the formation of _rust_ in the bore, and, as a consequence, _corroded barrels_, calling for the excessive use of wire gauze, or even more drastic treatment, thereby causing unnecessary wear. (ii) =Internal Fouling.=--Internal fouling can be removed satisfactorily by the use of boiling water [Sec. 4, para. 6 (ii)]. If for any reason this method of cleaning cannot be used, the barrel will “sweat,” and a hard black crust of fouling will appear in the bore. This will turn to red rust if not removed, and the rifle will then require repeated cleaning with flannelette, and probably with gauze, for a time, which will vary according to climatic conditions and the state of the bore. (iii) =Superficial Fouling.=--Superficial fouling is readily removed, when warm, by the use of a pull-through and flannelette, but if it is allowed to remain long in the barrel, it will become hard and will have a corrosive effect equal to that produced by internal fouling. 3. =Nickelling.=--The appearance of nickelling, or _metallic fouling_, should be watched for. It is caused by a portion of the cupro-nickel of the envelope of the bullet being left on the surface of the bore, and appears as a whitish streak on the lands, or as a slight roughness on the edge of the grooves. If it is deposited near the muzzle or the breech, it is visible to the eye when the bore is clean, but in the centre of the bore it can only be detected by the use of the gauge plug. It is a cause of inaccuracy, and if a rifle for no apparent reason shoots badly, its presence should be looked for as a possible explanation. The soldier will make no attempt to remove it himself, but will hand his rifle to the armourer, or other qualified person, to be cleaned. Section =3=.--Materials used for Cleaning Arms. =1. Pull-Through= (Fig. 1).--(i) A pull-through fitted with a weight, and an oil-bottle to contain Russian petroleum, are carried in the recess in the butt of the rifle. The pull-through is made with three loops. The first--_i.e._, nearest the weight--is for the gauze when used; the second for the flannelette; the third is provided merely as a means of withdrawing the pull-through in case of a jamb. Neither flannelette nor gauze should be placed in this loop. When signs of wear appear, a new cord should be supplied, to avoid the risk of the pull-through breaking in the rifle. If a breakage does occur, the rifle must be at once taken to the armourer. No attempt should be made by the soldier to remove the obstruction.