32 MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



embedding agricultural specimens in methacrylate resins was under- 

 taken in 1937 by C. E. Sando of the United States Department of 

 Agriculture as part of a project for the investigation of processes for 

 preserving specimens of materials related to agriculture in as nearly 

 natural condition as possible. Progress on this work was summarized 

 by Knight in his annual reports (11, 12, 13, 14)- In 1942 Fessenden 

 and Sando (6) published a review of the investigations conducted by 

 other workers in this field and of the procedures and results reported 

 by them. 



EQUIPMENT AND SUPPLIES 



In order to carry out the embedment of specimens in methacrylate 

 resins safely, it is necessary to employ a fume hood or a similar enclosed 

 space provided with an exhaust fan or other adequate means for remov- 

 ing the vapor and preventing its spread into the room where the work 

 is being performed. This fume hood, or ventilated enclosure, should 

 be large enough to hold two steam or electric ovens, and at the same 

 time leave room for an electric hot plate and the various other pieces of 

 apparatus listed below that are required for preparing the plastic casting 

 sirup. It is also good practice to provide sufficient general ventilation 

 for the work room itself so as to avoid danger of building up undesirable 

 concentrations of the methacrylate vapor that tends to escape from 

 molds, flasks, and other containers. 



Enclosed exhaust systems should be arranged to draw air and vapors 

 toward the rear of the enclosure away from the operator — not upward, 

 since this would not protect the operator. Such an exhaust system 

 should also be arranged to take vapors from the lowest level where 

 heavy vapors may accumulate. 



All electrical equipment used in the exhaust system should be of a 

 type approved under Article 500 of the National Electric Code. 



Where an adequate exhaust system is not provided, each operator 

 exposed to poisonous vapor should be protected by an air-line gas mask 

 with full face protection supplied by air pumped with approved ap- 

 paratus from a source known to be safe. 



Persons exposed to poisonous liquids or vapors that can be absorbed 

 through the skin should wear rubber or Neoprene gloves. 



A 20-pound approved dry-chemical fire extinguisher should be 

 mounted near the exit door. 



Conspicuous "no smoking" signs should be exhibited near entrances 

 to and within rooms where the work on preparation of plastic and em- 

 bedment of specimens in methacrylate plastics is carried on, and the 

 u no smoking" rule should be rigidly enforced. 



An electric refrigerator, or its equivalent, is necessary for storage of 

 the monomeric liquid and the partially polymerized sirup. A small or, 

 preferably, medium size, household type of refrigerator is adequate for 

 work by one or two persons. 



Two ovens, either steam or electric, are needed for heating the plastic 

 castings during the two stages of polymerization. These ovens, if elec- 

 trically heated, should be equipped with external contact points and 

 should have enclosed heating elements to minimize the fire hazard. 

 They must also have spring catches to keep the doors closed, rather than 



