A  highly  interesting  process  for  the  conversion  of  acetic acid  and acetates  to  citric  acid  by yeast  was  patented  by Boehringer  (10).  This  process  is  based on  the  original discovery  of  Wieland  and  Sonderhoff  (53) who  found  that aerated yeast  cultures  produced  both  succinic  and  citric acids from acetates.  A dilute solution  (0.2 N)  of  sodium or calcium acetate is fermented with yeast under highly aerobic conditions maintained  by stirring the solution vigorously  in the presence of  air or oxygen.  Eight hundred and Bty  grams of  citric  acid  and  230  grams  of  succinic acid were  obtained from  6000 grams of  acetic acid during a fermentation period of  12  hours.  The  chief  importance  of  this  discovery  lies  in the fact  that a  submerged yeast  growth  is  employed for  the process, making  possible the use  of  tanks or vats  as culture vessels.  The reported yield of  citric  acid is  low, but further research  might  reveal  conditions  that  would  lead  to  im- provements in  this respect. LABORATORY  METHODS  OF  CULTURING  SURFACE MOLDS  IN  TUBES  AND  FLASKS Zender  (56)  recently patented  a process for  the production of  citric  acid by mold fermentation in which the acid may be crystallized  directly from the culture  solution,  thus eliminat- ing the usual step of  first  separating  the  acid as the calcium salt.  The  mold-fermented  culture  solution  is  fermented with yeast  in the presence of  a soluble calcium compound to remove  the  residual  carbohydrate,  the  calcium  is  removed with  oxalic  acid,  and  the  citric  acid  is  then  recovered  by crystallization. Properties and Uses  of Citric Acid Citric acid was first isolated  in the solid state by Scheele  in 1784  from  lemon  juice.  It  crystallizes  in  large  rhombic prisms  containing  one molecule  of  water  of  crystallization and has the  formula  CsHg07,H20.  The  anhydrous  form  of the acid, which is now  commercially available, crystallizes  in monoclinic prisms.  It is readily soluble  in water, moderate:y in alcohol, but only sparingly in ether.  The water of  crystal- lization  of  the hydrated form is entirely lost at 130";  it melts at 153"  and, on further heating above 175", decomposes into aconitic  and  itaconic  acids, citraconic  anhydride,  carbon dioxide,  and  acetone,  Chemically,  citric  acid  is  a  tribasic acid forming three series of  salts which are well defined.  The alkali  salts are  soluble  in  water,  the  others  are mostly  in- soluble. Citric acid is used  in the manufacture of  citrates, flavoring extracts,  confectionery,  soft drinks,  effervescent  salts, as a silvering  agent  and  as  an  ink  ingredient  in  engraving,  in dyeing  and  calico  printing,  and  in medicine. According  to the United  States Department  of  Commerce,  about  65  per cent of  the domestic consumption was recently reported to be used  for  medicinal purposes, including  the manufacture  of citrates, 15 per cent in foods, 9 per cent in candy, and smaller amounts in silvering, engraving, as an ink ingredient, and in dyeing  and  calico  printing.  Recent  research on  synthetic resins of  the alkyd  type  revealed  the  importance of  citraconic and  itaconic acids  and  their anhydrides  as  raw  materials. Substantially better yields of  these products  from citric acid were  obtained  recently;  an enormous  potential  use  of  this acid  (9)  is  thus  indicated.  The  use  of  citric  acid  in  the manufacture  of  edible  synthetic  ester  resins  which may  be employed  as  substitutes  for chicle  was  suggested  by  Ellis (21).  The use of  citric acid  in  Italy in  the manufacture of 1-phenyl-3-methylpyrazolone  which  is  used  as  an  interme- diate in the production  of  antipyrine and  certain  azo  colors was  reported by Corbellini (17). Natural Citric Acid Industry Citric  acid occurs  in many  plant  tissues,  especially  those of  the  citrus  variety.  In  citrus fruits  and in  sloes,  cran- berries,  etc.,  it  occurs  free  and with very  little malic  acid; in  fruits  such as  the  cherry, strawberry, and  raspberry  it occurs with an approximately equal proportion of  malic acid. The chief  commercial sources for the natural variety of  acid are lemons, limes, and pineapples. Another potential source of  large quantities of  citric acid is tobacco waste but, so far as is  known,  no  commercial development of  a  process making use of  this material has yet occurred, although several patents have been granted to Shmuk (62). Italy  still  produces  the  largest  quantity  of  natural  citric acid;  the  only  other  important  sources are  California,  the West Indies,  and  Hawaii.  The  Sicilian  citrus  by-products industry  was described  in  detail  by  Cruess  (I@,  Molinari (Sti),  and  Galeano  (b7),  so  that  only  the more  important features of  this industry will be mentioned here. The  larger  part  of  the  citrus fruit  grown  in  Sicily  is  pri- marily  for  export  in  the  fresh  state.  The  normal  annual production of  lemons in Sicily is 300,000  tons, but, unless the fresh fruit market is unfavorable, little normal fruit goes into the  by-product  industry.  However,  the  proportion  of  in- ferior fruit grown in Italy is very high  (30 to 50 per cent) so that large quantities are available for the production of  lemon oil and calcium citrate. Most of  the Italian  calcium citrate was formerly exported, but since 1921 large quantities of  this raw material  have  been consumed  for  the manufacture  of citric acid in the domestic citric acid industry. 柠檬酸工业英文文献和中文翻译(7):http://www.youerw.com/fanyi/lunwen_30316.html