270             The Nutritive Value of Alkali-treated Cereal Straws

2. The strength and composition of the residual liquor + first wash
water after alkali treatment of wheat straw :

From the above results, it may be observed that there was a small amount
of sodium carbonate present in the caustic soda solution originally used for
the treatment but, after treatment, the major portion of the recovered alkali
was present as sodium carbonate, which would indicate that the caustic soda
was extensively converted into sodium carbonate on exposure during the 20
to 24 hours soaking of the straw. When the alkali content in the ori-
ginal solution and the recovered liquor was calculated as sodium carbonate,
it was found that after one treatment of wheat straw, 65 per cent of the
alkali could be recovered. In a similar experiment with paddy straw, 63
per cent of the alkali used was recovered.

In order to test how effectively the recovered alkali could be used for
the next treatment, the following experiment was undertaken : To the
alkali solution recovered from the treatment of paddy straw, 10 gm. of solid
caustic soda were added. The added caustic soda was actually 50 per cent
of the alkali present in the solution used in the first treatment. A second
lot of 200 gm. of paddy straw was treated with the regenerated alkali solu-
tion. At the end of the treatment the alkali was recovered in the same way
as before and the recovered alkali was found to be about 66 per cent of its
original strength. By similar replenishment of the recovered alkali from the
second treatment, a third lot of straw was treated. The residual liquor
recovered after the third treatment was found to be very thick and viscid,
and, as its effectiveness was doubted, no further attempt to re-use the
alkali was made. The treated straws from the second and the third batch
were analysed to determine (a) the recovery of dry matter and (b) the per-
centage of crude fibre. The results have been set out in Table VII along
with similar figures obtained for the first lot.

                                              TABLE VII

Composition of paddy straw after treatment with regenerated recovered alkali
                                                solution

It is apparent from the data given above that the quantitative change in the
composition brought about in the straw by the recovered and regenerated
alkali solution was practically similar to that of the first batch of straw treated
with the caustic soda solution. Moreover, the composition of the crude
fibre of the three lots of straw treated in the laboratory agrees well with that
of the paddy straw which had been treated on a large scale and with which
a feeding experiment had been actually carried out. The present