After digestion, the Taylor tubes are removed and allowed to cool. A 5-ml volume of 1N HC1 is added to dissolve any calcium sulfate precipitate that may exist and the volume is then made up to 25 ml. To dissolve the solids, the samples are warmed and aliquots taken for various elemental determinations. After the blocks have cooled for 2 hours, the next digestion can be initiated, allowing for 2 digestions in a 24-hour period, resulting in the preparation of 288 samples per day. CONCLUSIONS
This method has been tested in the Agassiz Soils Laboratory during the last four years. The digestion of over 5000 samples, with varying types of plant materials, allowed comparison with the Kjeldahl digestion method, and no significant differences in elemental determination were found. However, it is important to note that while the digestion system was experimental, using various acid mixtures, one explosion occurred. Although the Taylor tubes were shattered to a distance of 2 meters, the explosion caused no damage to property or operator. It resulted when an insufficient amount of nitric-perchloric acid mixture was used without predigestion. The material consisted of 1 gram of silage corn and 4 cc of acid mixture. After an hour of heating, the material appeared paste-like. Then a spark was seen, immediately followed by
an explosion. The thermometer in the aluminum block recorded 140 “C, a temperature well below the boiling point of perchloric acid (203 “C)which is normally considered the critical temperature for violent reactions. The possible cause of the explosion was the formation of an alcoholic ester, and this, and similar reasons, have been given by Deiss (5) and Sweasey (2). However, use of the same material, with a higher amount of acid mixture, resulted in normal digestion. Although the use of aluminum blocks and a temperature controller are helpful in reducing the dangers of explosion, it is recommended that the following precautions be taken : (1) Predigest the samples overnight at room temperature. (2) Samples containing alcohols, glycerols, or esters should be presoaked with acid mixture for longer periods of time and digested at low initial temperatures. (3) Use a minimum 10 ml of acid mixture to 1 gram of plant material. RECEIVED for review August 16, 1971. Accepted September 15, 1971. Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the named product. ( 5 ) E. Deiss, Z . A n d . Chem., 107, 8 (1936).
Conversational Text Editor for a Laboratory Minicomputer Herbert P. Yule’ Activation Analysis Section, Analytical Chemistry DiGision, National Bureau of Standards, Washington, D.C. 20234
To UTILIZE an available Varian 620i minicomputer for data acquisition and manipulation and for result computation ( I ) for the NBS Activation Analysis Section, considerable programming in the assembly language, DAS, is required. To facilitate the preparation of source program tapes, the debugging of these tapes, and updating of programs, a conversational editing program is reported here for other 620i users who may wish to acquire copies of the program. Modification of source program tapes may be performed under control of a program which permits reading the source tape line by line and allows the operator the options of inserting, modifying, or deleting lines of program text. As each line is completed, it is punched into a new source tape. This procedure is rather cumbersome since modifications must be made in order of appearance in the text, and errors made during source tape editing may necessitate repeating the source tape modification procedure. An alternate method of editing text is to store it in core and modify the text as desired without regard to the order in which modifications are made, and without reading and punching tapes. This “conversational” method is more convenient and much quicker to use. In programming for our system, a complete source program is stored on a rotating drum memory and read by a subroutine which has been appended to the DAS assembler. No source program is punched until a permanent copy is needed. An additional advantage of the program is that it was purposely written to accept commands very similar to those of a widely available commercial conversational text editor ( 2 ) ; anyone familiar with this time sharing 1 Present address, NUS Corporation, 4 Research Place, Rockville, Md. 20850
(1) Nat. Bur. Stand. ( U . S . ) ,Tech. Note 548, Dec. 1970, pp 124-139.
(2) Tymshare Manuals Reference Series, “Editor,” Tyrnshare, Inc., Palo Alto, Calif., July 1969.
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service can quickly learn to operate the presently described text editor. Frequent use of this service was made during preparation of our text editor. The present program is configured to our hardware: 16 bit, 8192 word memory, 30720 word rotating drum memory, high speed paper tape reader, and model ASR33TZ Teletype. However, modifications to other configurations are possible. Program size, including the drum driver, is about 3300 words (octal), and the pointer table occupies locations 200-206 (octal). Remaining core may be used for text. Text may be entered from the keyboard, tape reader, or drum. As text is entered from the keyboard, it may be edited by deleting characters or lines. Existing text may be appended via the keyboard or tape reader. Text stored in core may be listed, punched, or transferred to the drum. Lines of text may be addressed by line number, and search routines permit quick and ready determination of line numbers. Addressed lines may be modified, deleted, or listed, and text may be inserted before an addressed line. The line address is easily incremented or decremented. Copies of the source program and operating instructions are available from the author. The program is relatively new, and cannot be guaranteed as bug free. Nevertheless, recent experience with the program has shown it to work well and be a great aid in programming the computer.
RECEIVED for review June 28, 1971. Accepted September 22, 1971. In order to specify procedures adequately, it has been necessary to identify commercial materials in this report. In no case does such identification imply recommendation or endorsement of the National Bureau of Standards, nor does it imply that the material identified is necessarily the best available for the purpose.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
