Hydrogen sulphide production, measurement

Variation of the nature of the gate electrode results in the different types of FET. For example, in the metal oxide semiconductor FET (MOS-FET) palladium/palladium oxide is used as the gate electrode. This catalyti-cally decomposes gases such as hydrogen sulphide or ammonia with the production of hydrogen ions, which pass into the semiconductor layer. An enzyme may be coated on the palladium, e.g. urease, which catalyses the production of ammonia from urea and thus provides a device for the measurement of this substrate. 

The results of earlier workers on this subject were vitiated by experimental errors. These arose from the circumstance that union takes place quite rapidly at temperatures below the boiling-point of sulphur, and is not conveniently measurable at higher temperatures. Consequently experiments were always made in presence of liquid sulphur, which possesses the property of dissolving hydrogen sulphide, so that the products of reaction are removed to a greater or less extent depending on the amount of sulphur in the reaction bulb. 

---