A plastic capsule technique for the combustion calorimetry of volatile or chemically reactive compounds: The heat of combustion of polythene
There have been several approaches to these problems, but the most efficacious and widely used has been to introduce the substance (usually a liquid) into glass ampoules of suitable size and then to seal these15• Such sealed ampoules completelysatisfyconditions (a) and (b) above, but they have a number of disadvantages. The technique of manufacturing and filling them requires considerable skill, and, even at best, is a hit-and-miss affair. They have to be strong enough to withstand the pressure (30-40 atm) of oxygen in the bomb without bursting and yet not so strong that they fail to break on ignition of the auxiliary burning substance. In general, they fail to satisfy condition ( c) in that the risk of explosion and incomplete combustion is fairly high35• An ingenious way of minimizing these latter difficulties is due to Thompson6• Again, sealing of the ampoules is a very delicate operation since it is liable to cause a certain amount of decomposition of the sample. Finally, there is always the danger that the melting glass may occlude some intermediate products of the combustion, though apparently this does not in general occur to any significant extent5• The above considerations have led us to search for a Straightforward and reliable alternative to the glass ampoule technique, and we believe we have found such in the following simple method for making closed polythene capsules of any desired size or shape.