According to R. von Demuth,4 dilute sulphuric acid has replaced sulphur dioxide as hydrolysing agent in some of the American factories. To obviate destruction of the sugars formed, the process is accelerated as much as possible. The steaming lasts only long enough to hydrolyse a certain proportion of cellulose and produce a condition of equilibrium (between sugar destroyed and sugar produced); this takes about an hour. The hydrolysed wood is then extracted in a diffusion battery, pressed, dried, and used as fuel.

The extract, after being nearly neutralised with lime, is fermented with yeast that has been cultivated in a rye and malt mash; cooked malt combings are used as yeast nutriment. About 7 3 to 9 5 litres of alcohol (100 per cent.) are obtained per 100 kilos, of dry wood: this corresponds with 16 to 21 imperial gallons per ton. In addition, a small quantity of turpentine oil, about 003 per cent., is recovered as a by-product. Only traces of fusel oil and esters are present in the alcohol produced.

1 U.S. P. 938308 of 1909. 2 A. Hirsch, J. Ind. Eng. Chem., 1912, 4, 479. 3 Chem. Tr. J., 1918, 63, 103. 4 Zeitsch. angew. Chem., 1913, 26, 786.

According to E. Hagglund,1 only very dilute acid is likely to be commercially successful for the hydrolysis of wood in the making of alcohol. Dilute sulphuric acid of strength 0 25 to 1 per cent, can be employed, and the best temperature is 175°. The proportion of wood to acid may be as high as 1 to 3. Under these conditions the yield of alcohol was found to be from 75 to 85 litres per ton of wood (pine or fir). The use of sulphurous acid or calcium bisulphite decreased the yield to about 40 litres and 60 litres per ton respectively. Comparison experiments carried out with much stronger sulphuric acid (70 per cent.) indicated that under the most favourable conditions as much as 158 litres of alcohol per ton could be obtained, but the greater cost of the acid more than offset the increased yield of alcohol.

Some lengthy and careful investigations have also been carried out by F. W. Kressman.2 He concludes that for commercial working the most satisfactory conditions for the digestion of the wood are: Pressure, 7 1/2 atmospheres; duration of the digestion, twenty minutes from the time the working pressure is attained; ratio of water to dry wood, 125 to 100; ratio of acid to dry wood, 2 J to 100. Under these conditions, white spruce yielded 23.6 per cent. of total sugars, calculated on the dry wood, and 71.4 per cent. of the sugar was fermentable. The yield of alcohol was 854 per cent. of the weight of dry wood. Larch was found to yield much galactose, which is not fermentable with ordinary yeast.

Reviewing the present position of this industry, Tomlinson regards it as one of relative stagnation, due partly to the fact that operations have been started prematurely, with little regard to the commercial conditions involved.3 The fact, however, that several million gallons of alcohol have actually been produced from wood waste, and that at least two plants have been operating more or less continuously over a period of years, justifies the belief that ultimate success is assured.

It was originally assumed that almost every sawmill represented a possible location for the establishment of an alcohol plant. There were large numbers of sawmills at which the disposal of the wood-waste was a problem, and even an element of expense. Hence it was assumed that this waste could be purchased at a purely nominal figure, and so an almost endless chain of alcohol-producing plants might be established. It was soon found, however, that while there was no question regarding the number of sawmills or the quantity of waste wood produced, nevertheless there were very few mills at which the conditions were altogether favourable for setting up the extensive plant which the manufacture of alcohol requires. The "life" of the lumbering operations may be uncertain, the water supply deficient, labour or transportation facilities unfavourable, and so on. Moreover, the lumberman who has a suitable "location" soon recognises his advantage and exacts his price. The alcohol maker must pay it, for the plant when once established has no other source of supply. Sawdust and other waste wood is bulky and difficult to handle and transport; so that, in practice, it must be treated at the place where it is produced.

1 J. pr. Chem., 1915, 91, 358. 2 J. Ind. Eng. Chem., 1915, 7, 920. 3 Chem. and Metall. Eng., 1918, 19, 552.

For these various reasons, the authority quoted considers that if the industry is to be greatly extended, a modification of procedure will be necessary. In general, the sawmills should produce the sugar solution from the waste wood, but should not ferment and distil it. They should evaporate it to a syrup or molasses, which could then be conveyed to suitable distilleries working on a large scale, where it would be fermented and distilled under the most favourable conditions.

This would mean that only a molasses plant would need to be installed at the sawmill, instead of the complete distillery outfit. Smaller units, could be worked economically; less skilled labour would be required; and the plant would be free from revenue regulations. Further, if the molasses product is sold to those already engaged in the distilling industry, many market and other trade difficulties are removed. Complete installations for the production of alcohol would, of course, still be erected in localities where the conditions were specially suitable.

Naturally, the important factor in the development of the industry, as thus outlined, would be the cost of the syrup obtained, as compared with that of cane-sugar molasses. The following particulars of actual working costs are given.

Working for twenty-two days in 1913, at three-fourths of the full capacity, the Fullerton plant, previously mentioned, dealt with 6125 tons of green waste wood containing 48 per cent. of moisture, and yielded 1,688,600 gallons (U.S.) of sugar solution at about 103 per cent. strength. The total cost was 31.8 cents per 100 gallons. The molasses obtained by concentrating 100 gallons of the sugar solution down to 12 1/2 gallons cost about 3 cents per gallon, including cost of evaporation. This is much lower than the cost of cane molasses. But whereas one gallon of the wood molasses yields only about 0 39 gallon of proof spirit (U.S. proof), cane molasses yields about one gallon. Proper chemical control, however, might result in obtaining a product equal to cane molasses. "There is thus within reach an almost unlimited supply of wood molasses which the distiller can readily convert into alcohol, with little or no modification in the ordinary distillery equipment."1

In W. P. Cohoe's process, the conversion is done in two stages, First, steam is used alone; this produces some acetic acid, which is collected. Then a mixture of steam and gaseous hydrochloric acid is introduced to complete the conversion.2

Gazagne and de Demuth have described the following procedure.3

Peat, or sawdust, or other wood waste, is saccharified by heating under pressure with a mineral acid. The product is then systematically extracted with hot water, or with vinasse liquor from beet-sugar manufacture, in a battery of extraction-vessels, as in the extracting of sugar from beets. The solution thus obtained is neutralised with ammonia or alkali hydroxide, and fermented. To improve the fermentation, yeast is used which has been specially acclimatised to liquors from cellulose materials containing tannins; and yeast nutriment is added in the form of saccharifiable substances relatively rich in nitrogen and phosphorus. These substances may either be included with the charge in the autoclave, or saccharified separately and added to the liquor after the extraction is completed.

Mention may be made here of lævoglucosan, obtained by Pictet and Sarasin on distilling cellulose or starch under reduced pressure. This product is hydrolysed by dilute sulphuric acid to glucose, which could be used as a source of alcohol.4 As the lævoglucosan could be obtained in quantity, the authors suggest that it may prove to be utilisable for the industrial production of alcohol.