BASIC GLASS-WORKING OPERATIONS

Basically, we must not permit the cryogenic fluids and their vapors to contact any part of the body. The eyes and face are particularly vulnerable. Accordingly, all operations must be conducted with adequate eye and face protection. All personnel who work with low-temperature systems should wear safety glasses at all times. Further, where there is a possibility of face contact with cold vapors or liquid, a full face shield or perhaps a face shield and hood should be worn. Care must be taken not to permit rising vapors from lighter-than-air gases to enter the shield. As noted in the previous section, only inert hoods such as those made of Teflon or KelF should be worn to avoid skin contact with fluorine. 

Earlier on we have seen that indicators are unsatisfactory for measuring pH of solutions which are colored. We have also seen that for works which require absolute accuracy, indicators are not a good tool for pH measurement. Such situations call for electrometric determination of pH. For a student of biochemistry, probably the most familiar instrument is the pH-meter. Its operation is quite simple it consists of a glass electrode which when dipped into a solution develops an electrical potential depending upon the hydrogen ion concentration and this potential is read off the display which is calibrated into a pH scale. Let us try to understand the basic principles underijdng the working of a pH meter. 

---