Lederberg, Esther M. to Cavalli-Sforza, Luca Luigi
June 13, 1965

WhoX WhoX

Click image or caption to return

d0xxx EML to LLCS (velveteen) 6-13-65 66-69

To ease reading, a transcription of the first paragraph (above) follows.

d0xxy EML to LLCS (velveteen) 6-13-65 66-69
Return

If velveteen of acceptable quality that had not been waterproofed ("scotch-guarded") was unavailable, filter paper could be used temporarily to simultate replica plating. However, just as there were different levels of quality to velveteen, there were also different levels of quality in filter paper. These kinds of problems with filter paper were well-known to chemists who had studied inorganic quantitative analysis.

Inorganic quantitative analysis has three major branches of study:

Gravimetric analysis consists of collecting a precipitate from solution using filter paper, then measuring the quantity of precipitate. To measure the quantity of precipitate, the precipitate in the filter paper is thoroughly dessicated, then slowly burned in accurately pre-weighed numbered crucibles with numbered covers. If the exact weights of the crucibles, covers, and the ash-weight of the filters is subtracted from the total weight, the remaining weight is the weight of the precipitate. For gravimetric analysis to provide accurate weights, several factors are important, such as there being no reaction of the precipitate with the environment; and most crucially, a precise knowledge of the exact ash-weight of the filter paper. The quality of the filter paper is analogous to the quality of the velveteen used in replica plating. For example, heavy metals in filter paper could act as a poison to bacteria or interfere with measurements being assayed in an experiment.

It was well known that replica plating was superior to other similar methods such as using filter paper, prongs, etc, but virtually all researchers recognized that replica plating was the best method to replicate many colonies at one time.

Back