COOL DOWN to -2(ra
The NEW KR 30 Refrigeration Unit makes ANY circulator into a low-temperature circulator for only $250.00 Connected to a Haake Circulator, t e m p e r a t u r e is pulled down to —10° C in less than 30 minutes. Controlled temperatures down to — 20° C are achieved by using the control features of the circulator connected to this unit. Control to ±0.01° C is achieved when used with a Haake Circulator. Portable and compact, the KR 30 incorporates a Vi H.P. Tecumseh compressor. The Freon 12 refrigerant is circulated through an in ternal heat exchanger, through which the liquid to be cooled is pumped. Any circulator can be easily connected using suitable lengths of rubber hose. For additional information, write for Bulletin 37.
PolyScience Corporation
PSC
INTERNATIONAL DIVISION
.
909 PITNER AVENUE EVANSTON. ILLINOIS 60202 312 475-2909 Pittsburgh Conference March 4-8, 1968
Circle No. 186 on Readers' Service Card
ONE MUT PER MILLION Model HE 43 Scries OR I LAB and HF 373 Series DR I TRAIN
STANDARD AND CUSTOM CONTROLLED INERT ATMOSPHERE RECIRCULATING GAS PURIFICATION SYSTEMS FOR SPACE AGE R & D AND PRODUCTION
VACUUM/ ATMOSPHERES CORPORATION
Ο, aid HO (Optional N , Removal Capability) For full information write or call: (area code 213) 983-0763.
ïm&
7356 GREENBUSH AVENUE, NORTH HOLLYWOOD, CALIFORNIA
Circle No. 83 on Readers' Service Card 36 A
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ANALYTICAL CHEMISTRY
REPORT
Petten have determined the compo sition of over two hundred coins from Asia Minor made of electrum (a gold-silver alloy). Another interesting problem which can be studied by a combina tion of neutron activation and Xray fluorescence is that of surface enrichment (25). This is a term which is commonly used by archae ologists to denote the changes in composition which occur near the surface of objects made of noble metal alloys during burial in the ground for a prolonged period of time; the baser elements in the al loy are slowly leached out, so that the surface is said to become en riched. This phenomenon has long been known on a purely qualitative basis, but it is now possible to mea sure quantitatively the extent to which this surface enrichment can occur. Sutherland and Harold (26) have examined a number of early copper coins minted under the Em peror Diocletian, and they found that the average silver content de termined by neutron activation analysis was 3.7 per cent, whereas the silver content on the surface as given by X-ray fluorescence analy sis averaged about 5.6 per cent, thus indicating the extent to which sur face enrichment in terms of silver had occurred. A similar study of a British Bronze Age gold tore was made by Hall and Roberts (27), who found by neutron activation analysis an average composition for the alloy of 73.4% gold, 10.1% silver, and 16.5% copper, and by X-ray fluo rescence analysis a surface composi tion of 88.7% gold, 8% silver, and 3.3% copper. This clearly shows the degree of surface enrichment in terms of gold, which has taken place as the result of the slow leaching out of silver and copper from the alloy. I t may be expected that further work will produce analytical results which will throw light on the actual processes whereby sur face enrichment is produced. Another sophisticated method of analysis which has also been ap plied to archaeological investiga tions is the electron beam microprobe analyser. The value of this new technique in the analysis of an cient glass has been shown by Brill
