58 RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



Aside from the bast fibers just discussed, both Asclepias and Apocy- 

 num yield a surface fiber that may be obtained from the seed. But it is 

 unlikely that this could be gathered from plants grown primarily for 

 their rubber, since harvesting would probably take place before the 

 fiber would have time to develop, and aside from this it is of but low 

 value. 



Paper pulp. In case the fiber is not of more value for the manu- 

 facture of cloth, it may be utilized as a source of paper. A pulp pre- 

 pared from one of the eastern milkweeds, probably Asclepias syriaca, 

 has been made up into a fair quality of paper at one of the leading 

 factories. This was done many years ago and the matter dropped, 

 since it was not profitable to grow the plants for this purpose alone. 

 The only paper made from milkweed during the present investigation 

 was manufactured from the desert species (Asclepias subulata) by the 

 same firm and the product found to be much superior to that formerly 

 examined. The plant from which this sample came was collected at 

 Sentinel, Arizona, September 29, 1920, under No. 1054; it is illustrated 

 in plate 1. The sample consisted of the very hard, dry stems, which 

 were practically devoid of foliage, as is generally true of mature stems. 

 The material was worked up by the factory, following the usual 

 procedure. The fiber expert for the company states that the report 

 of the laboratory is very encouraging, that the milkweed has all the 

 appearances of making a good pulp, and that the hand-made sheets 

 show a long, soft fiber which under the microscope resembles linen. 

 The processes used in the preparation of the paper were as follows: 



EXPERIMENT 1. 



1. 456 grams of material as received cooked with 10 per cent (45.6 grams) 



caustic soda for 3 hours in an open kettle. 



2. This material run through wringer rolls to crush out. 



3. Crushed material washed clean and dried out. Weight 196 grams. 



4. Material thus washed next cooked in closed kettle with 10 per cent 



(19.6 grams) lime for 5 hours at 30 pounds pressure. 



5. This cooked material washed and beaten in beater and run out on 



hand moulds. 151 grams of unbleached paper obtained. 



6. This 151 grams unbleached paper next bleached with bleach solution 



made from an amount of bleach powder equal to 7 per cent 



by weight of the 151 gra ms of the unbleached fiber. This gave 



130 grams of bleached paper. 

 Yields: 



From material as received to washed, crushed, bone-dry fiber (end 



of operation 3), 43 per cent. 

 From material as received to unbleached paper (end of operation 5), 



33 per cent. 

 From material as received to bleached paper (end of operation 6), 



28.5 per cent. 



