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Object Name: countercurrent distribution machine
Date: circa 1963
Inventory Number: 2014-1-0230
Classification: Distribution machine
Subject: chemistry, biology
Inventor: Lyman Creighton Craig
1906 - 1974
Maker: H. Otto Post
fl. 1930-1970
Cultural Region: United States
City of Origin: New York
City of Use: Cambridge
Dimensions: 240 × 70.4 × 157 cm (94 1/2 × 27 11/16 × 61 13/16 in.)
Materials: steel, glass, aluminum
Description: The core of the machine consists of an extraction (or distribution) train made of 520 glass equilibration cells. Each cell acts like a specially-designed separatory funnel. The cells are all linked together, glass to glass with no rubber or plastic connections, and placed on four rows (130 cells per row). Access to each separate cell is made through an opening closed with a flat ground-glass stopper held in position by a simple spring clamp (for easy and rapid access). The whole train is mounted on a mechanized support structure so that the whole train can rock or tip back and forth at a constant speed and a specific angle in order to distribute the extracting solvent and the sample mixture. The train is enclosed in a stainless steel-framed case with sliding glass windows. The fumes emanating from the use of solvent is vented through an opening on the top of the case. The case is basically used as a hood, which would have been connected to the laboratory hood vent.

The mechanized support structure is driven by a motor located below the case. It is designed to produce simple tipping movements to adequately position the extraction cells. Underneath the case is also attached a stainless steel pan included for two reasons: (1) as a security measure (to make sure that when the machine operates unattended at night, the flammable solvent that might come out from the break of a glass cell will not accumulate at the bottom of the case) and (2) to wash out the cells at the completion of a run (using water and acetone). The whole machine is mounted on four wheels for mobility.
Signed: on a plaque: H. O. POST / SCIENTIFIC INSTRUMENT CO. INC. / 69-57 Juniper Boulevard South, Middle Village 79, N.Y.
Function: Countercurrent distribution separates parts of a mixture by taking advantage of the fact that different parts of a mixture dissolve more or less easily in different solvents. Some parts of the mixture will end up in a larger concentration in one solvent than another. This machine repeatedly mixes two solvents and moves them from one tube to the next. Gradually, different parts of the original mixture are gradually concentrated in a few of the tubes. Although it looks complicated, this machine just repeats one simple cycle over and over again.

Here's how to use it:
1) First dissolve the mixture that you want to separate in two solvents. What solvents you pick depends on what you are separating. The two solvents must be liquids that will separate, like oil and water. Technically, they must be "immiscible."

2) Pour some of the denser solvent into each tube in the machine and put all of the lighter solvent into the reservoir on the right side of the machine.

3) Once the machine is setup, an automatic timer system automatically controls the process. The tubes tip in one direction so that solvent from the reservoir pours into the first tube.

4) The machine then rocks the tubes back and forth to mix the two solvents and then waits for them to liquids to separate.

5) A motor tips again to pour the lighter solvent from the first tube to the second tube. It also pours new solvent into the first tube.

6) The machine repeats this cycle: adding solvent, shaking, allowing to separate, and transferring. Each portion of the lighter solvent moves from tube to tube, from the right side of the machine to the left. When it reaches the end of the first row, it is transferred to the second row, where it begins to move back to the right side. It can also be set up as a loop, so that once a portion of solvent reaches the last tube, it is transferred back to the first to begin again. The machine is typically allowed to run all night, sometimes making thousands of transfers.

7) As the portions of solvent move from one tube to another, different materials in the original sample move along at different rates. Gradually, after many transfers, different parts of the original mixture end up dissolved in different tubes.

8) After enough transfers, you can stop the machine and collect the small vials attached to each tube. These will contain different parts of the original sample. You can then evaporate the solvent and prepare the remaining material for analysis.

9) Once the sample have been collected, the machine must be cleaned. Once you remove, clean, dry, and reassemble the glass tubes, the machine is ready to be used again.

Historical Attributes: Countercurrent Distribution was developed in the late 1940s by Lyman Craig, a biochemist at Rockefeller University, and Otto Post, a machinist and glassblower. Craig needed to separate parts of an anti-malarial drug to study its make-up and understand how it was processed in the body. The countercurrent technique they developed allowed a faster and better separation of delicate organic materials than had ever before been possible.

Early countercurrent devices were small and powered by hand before Craig, Post, and others at Rockefeller improved them. The new machines were larger and operated automatically by time-controlled motors, which allowed them to run without any intervention from the experimenters. The machine displayed here is an example.

Countercurrent distribution became a primary tool in Craig’s lab and allowed advances in several areas of biochemistry. As researchers trained by Craig found jobs at other universities and in industry, they brought countercurrent distribution techniques with them. Machines like this one became an important part of biochemical research.

This particular machine was used by Professor Guido Guidotti here at Harvard. Guidotti was a student of Craig Lyman, the inventor of countercurrent distribution, at Rockefeller University. During his time at Rockefeller, Guidotti worked with other researchers to figure out the protein structure of human hemoglobin. They used a countercurrent machine much like this one to separate the samples they needed for the analysis.

Guidotti came to Harvard in 1963 where he continued his research on hemoglobin with this countercurrent machine. It was installed in a room by itself on the top floor of the Biological Laboratories building, where the noise of its motors and the fumes of the solvents would not bother anyone.

Primary Sources: Lyman C. Craig and H. O. Post, "Apparatus for Countercurrent Distribution," Analytical Chemistry 21 (1949): 500-504. (online here)

Lyman C. Craig, W. Hausmann, E. H. Ahrens, E. J. Harfenist, "Automatic Countercurrent Distribution Equipment," Analytical Chemistry 23 (1951): 1236-1244. (online here)
Provenance: Prof. Guido Guidotti used that machine at Harvard in the Biological Laboratories, located at 16 Divinity Ave, from the early 1960s when he arrived as a faculty until the early 1970s. When Guidotti moved to the Sherman Fairchild Biochemistry building in 1981, the machine followed but was no longer in use. The machine was moved to a storage location in the Northwest Labs when the Sherman Fairchild building was renovated in the early 2010s to accommodate the Stem Cell and Regenerative Medicine Department. The machine was acquired by the CHSI in 2014. It has been on exhibit in the Northwest Labs at Harvard since October 2015.
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