Straw is usually boiled in cylindrical rotary boilers. Some paper-makers, however, prefer to use one or other of the different forms of vomiting boilers already described. The use of a rotary boiler is open to certain objections. In the first place, it is doubtful if they are as economical of soda as the vomiting boilers, especially the more recent patterns; and, secondly, the rotation of the boiler so disintegrates the pulp, that a certain proportion of the cellulose, especially those fibres which are short, is liable to be lost during the subsequent treatment. It seems probable that the best results would be obtained if the rotation of the boiler were reduced to a minimum, in fact, sufficient only to produce thorough circulation of the liquor. The proportion of soda necessary to boil straw thoroughly is, for reasons already stated, greater than is the case with esparto. The amount varies from 10 to 20 per cent. on the raw material. {100} The different processes to which straw is subjected vary greatly. The following may be taken as a general indication of the methods employed. The straw is usually cut into short pieces of about 1–2 in. in length by means of an ordinary chaff-cutter. The cut straw is carried by means of a blast of air along a wooden tube or shaft into a chamber, the sides of which are made of coarse iron gauze. This chamber is itself inclosed in another chamber, in which the dust and dirt accompanying the straw collect. The clean straw is then placed in sacks and conveyed to the boiler-house. Owing to the bulky nature of straw, it is difficult to get a large charge into a boiler at one operation; it is therefore usual, after having filled it as completely as possible, to run in a portion of the lye required, and to turn on the steam for a few minutes. This has the effect of so far softening the straw as to make it lie closely at the bottom of the boiler and to allow of a further quantity being put in. This having been accomplished, the remainder of the lye required is run in, together with the requisite quantity of water, and the steam turned on. The pressure may vary from 10 to 50, or even 80 lbs. per sq. in., and the time from 4–8 hours.