Leak Detectors
Leak Detectors
Conservators embarking on a program of treatments with barrier-film contain- ers, particularly when the containers are handmade, will find a leak detector to
be a valuable tool. The detection of specific leak points can be accomplished in several different ways. It can be done by activating a battery-operated ultrasonic sound generator (35,000-40,000 Hz) placed inside a treatment container, and then searching for the leak point from the outside with an ultrasonic detector.
A detection system based on fluorescence works in a similar way. A tracer gas is released into the pouch (for example, by injection, with a gas syringe), and when an ultraviolet light is played over the exterior surface, leaks are detected as
a fluorescent glow. The cheapest and most popular device is the halogen leak detector, which is based on a refrigerant gas such as 1,1,1,3-tetrachloropropyl- ene that is released inside the chamber. The detector nozzle senses changes in the thermal conductivity of the atmosphere around the leakage point and gives off a characteristic squawk or squeal.
M onitoring Life Signs
Perhaps the most critical and the most difficult factor to be monitored is the extent and the completion of insect kill. Researchers have investigated a number of barely measurable manifestations of insect life signs but they have been unable to transfer their work into a monitoring methodology as satisfactory as
O perational Problems and Practices 37 O perational Problems and Practices 37
Some interesting approaches to measuring mortality directly have evolved. Koestler (Koestler and Mathews 1994) adapted a procedure developed by the U.S. Department of Agriculture (USDA) to determine insect infestations in wheat. The USDA created a highly sensitive FTIR analysis that could detect an output of about one part of carbon dioxide in one million parts of total gas per minute from a single rice weevil in 350 g of red wheat. Koestler was able to use his adaptation to follow the anoxic termination of insect life in museum objects.
A picture frame with suspected infestations was placed in a low-permeability pouch, and a steady increase in carbon dioxide was monitored for 5 days. The bag was then flushed with humidified argon until the oxygen content was below
0.1%, and new measurements were made. No carbon dioxide was detected after 16 days, and air was returned to the system. There was no additional for- mation of carbon dioxide over 11 days, which was taken to show that 100% mortality had been achieved.
A simpler, less sophisticated device to measure and monitor the respiration of a single insect was described by Carlson in 1995. The breathing of insects removes oxygen and releases carbon dioxide, but the net effect is a decrease in volume. Carlson designed an apparatus, contained in a constant-temperature bath, in
which a glass tube holding an insect is connected to a capillary containing a tiny droplet of oil. Movement of the droplet provides a life-sign indication of
metabolism. With some simple determinations of air pressure, temperature, and movement volume of the drop, it is possible to calculate the number of molecules the insect respires. The system is designed for amateur scientists and is inexpensive to put together, but a larger gastight container connected to a
capillary could make the unit suitable for determining whether infested material still harbors living insects.