cholanic acid, the dehydration product of certain bile acids that are found in all animals but not in plants. This steroidal acid has been found in trace amounts in petroleum samples believed to be more than 10 million years old and its presence has been used as evidence of the partial animal origin of these petroleums (C&EN, June 25, 1973, page 13). Now, however, its status as a natural product of exclu sively animal origin is being revoked. Scientists at the Agricultural Research Center of the U.S. Department of Agri culture have isolated 5β-cholanic acid from a plant source—the embryo of the jequirity bean. Dr. Nagabhushanam Mandava and coworkers found the compound while
attempting to isolate a growth-inhibit ing hormone from jequirity bean em bryos. In the March 1974 issue of Ste roids they explain that the compound was separated by ion exchange chro matography and converted into the methyl ester for analysis. Mass spectral and nuclear magnetic resonance analy ses, as well as melting point and opti cal rotation, were used to identify the product as the methyl ester of 5/3-cho lanic acid. 5a-Cholanic acid—which differs from the 5/3-acid in that it is trans at the A/B steroid ring junction whereas the 5/5-acid is cis—is quite common in plants. Dr. Mandava ran his sample along with known samples of both the cis and the trans cholanic acid methyl esters in mass spectral and
gas chromatographic analyses to con firm that he had isolated the 5β-acid. Whether 5/?-cholanic acid is unique to the jequirity bean or can be found in other members of the Leguminosae family or perhaps other related plant families has not been determined yet. As yet there is no clear reason why it should benefit the jequirity bean to have such an unusual plant acid, al though Dr. Mandava hopes that fur ther studies on this question will be conducted. But it is clear that 5/?-cholanic acid no longer may be considered a chemical trademark certifying the prehistoric presence of some type of animal. If one contemporary plant can produce this acid, then perhaps its an cestors could also.
Technology
Survey profiles worldwide desalination The poor economics of desalination to produce drinkable water has been a hard technological nut to crack. But that hasn't prevented desalination plants from being built. These two faces of desalination tech nology are evident in a newly issued survey made by the department of eco nomic and social affairs of the United Nations Secretariat in New York City. The survey, second of a series, covers operation of desalination plants throughout the world in 1968. A first survey, issued in 1969, covered the sit uation three years earlier. The current survey shows that largescale use of desalination plants in the world's arid regions has increased rap idly in recent years. However, the study indicates, there has been no dra matic breakthrough in costs. In fact, a report on the survey notes that no sig nificant changes in the economic or technological situation had become ap parent since the previous survey and suggests that the rate of development isn't great enough to justify a survey every three years. Excluding plants with capacity of less than 10,000 gallons pet 5 day, the survey covers 94 plants in 22 countries; there were 23 plants in the earlier sur vey. Total capacity of the plants is 61.5 million gallons per day. Of the plants reporting total water costs, the least expensive operations— two plants in Saudi Arabia—produced potable water for 53 cents per 1000 gal lons. However, fixed charges on invest ment in these cases were at a rate of only 5% (compared to the 10% the sur vey considers a minimum rate under normal economic conditions) and fuel cost was only 8 cents per 1000 gallons. For most of the plants, total costs amounted to more than $1.^00 per 1000 gallons. However, about 50% of the total water produced cost less than
$1.00 per 1000 gallons and more than 80% of the total produced cost less than $2.00 per 1000 gallons. Other gleanings from the survey pro vide a profile of worldwide desalination technology in place: • Of the 94 plants, 55 use multi stage flash distillation. Although used in only 60% of the total number of plants in the survey, the process ac counts for 88% of the total production capacity. • Multieffect distillation is used in 17 plants, but total capacity is only 1/10 that of multistage flash.
• Vapor-compression distillation is used in seven plants but accounts for only about 1% of the total water out put. • Only one plant uses reverse osmo sis, and brackish water is the feed. • Electrodialysis, on the other hand, is used in 14 plants, but mainly for small-capacity plants and always with brackish water as feed. • No plants use freezing. • Of the thermal distillation plants in the survey, 75% are dual-purpose plants, combining water production with generation of electricity.
Big rotary kiln will process Baltimore solid waste With Baltimore rising behind it, a 20- by 100-ft. kiln arrives in Baltimore harbor en route to incorporation into a pyrolysis system that will process 1000 tons per day of that city's solid waste. When it goes on stream in the third quarter of this year, the Landgard system, developed by Monsanto Enviro-Chem Systems, Inc., will recover, for sale, useful metals and a glassy aggregate that will be used by the city for road building. The sys tem, which will cost $15 million, also will generate 200,000 pounds per hour of steam that will be used for heating and cooling buildings in down town Baltimore.
March 18, 1974 C&EN
17
