A barium sulphate suspension in water is the universal contrast medium used for examination of the upper gastrointestinal tract. A simple barium sulphate/water mixture has several undesirable properties such as a tendency to sediment and unpalatability. Consequently many commercial barium meal preparations have been developed to obviate these unfavourable features.
The barium sulphate must of course be chemically pure, as the contaminant barium carbonate is extremely poisonous. The ideal barium sulphate/water mixture has yet to be developed, but the following properties are of utmost importance.

a) Particle size. Ordinary barium sulphate particles are coarse, measuring several millimetres in size, but ultrafine milling of the crude barium sulphate results in 50 per cent of the particles having a size of between 5 Ecm and l5lCm. As rate of sedimentation is proportional to particle size, the smaller the barium sulphate particle the more stable the suspension.

(b) Non-ionic medium. The charge on the barium sulphate particle influences the rate of aggregation of the particles. Charged particles attract each other and thus form larger particles which sediment more readily. They tend to do this even more in the gastric contents and consequently sediment more readily in the stomach.

(c) pH of the solution. The pH of the barium sulphate solution should be around 5·3, as more acid solutions tend to become more so in the gastric contents and consequently precipitate more readily in the stomach.

(d) Palatability. Undoubtedly ultrafine milling reduces much of the chalky taste inherent in any barium sulphate/water mixture, but many commercial preparations contain a flavouring agent which further disguises the unpleasant taste. The barium sulphate/water mixture is usually 1/4 weight/volume, and has a viscosity of 15-20 cp, but thicker or thinner suspensions may be used. Many commercial preparations contain carboxymethyl cellulose (Raybar, Barosperse), which retains fluid and prevents precipitation of the barium suspension in the normal small bowel.

The development of the double contrast technique has stressed the need for adequate mucosal coating and much of the present manufacturing efforts are devoted to achieving this. An excess of mucus and undue collection of fluid in the stomach greatly inhibit adequate coating of the gastric mucosa, as does hypermotility of the stomach.

To achieve double contrast examination of the stomach, air or carbon dioxide gas must be introduced and there is no doubt that introduction of air or gas via a nasogastric tube is the best means of obtaining a controlled degree of gastric distension. However, the passage of a gastric tube is an unpleasant procedure and is not acceptable to all patients. Consequently most radiologists use effervescent tablets (sodium bicarbonate 35 mg, tartaric acid 35 mg, calcium carbonate 50 mg) to react with the gastric contents to produce carbon dioxide. 

The amount of gas produced by these methods is variable and overdistension of the stomach in the double contrast technique associated with poor coating can be, from a diagnostic viewpoint, as disastrous as inadequate distension. Some commercial preparations contain carbon dioxide gas under pressure in the barium mixture, but usually the quantity of gas is not adequate to produce good double contrast meals. An anti-foaming agent may need to be added to some barium preparations to avoid the formation of bubbles.

Water soluble iodine-containing contrast media (e.g. Gastrografin) are of value when there is a suspected perforation or leakage of an anastomosis after operation. The low radio-opacity of the iodine compared with the barium, and the high osmolarity which results in dilution within the small bowel, make it of little value for routine use in investigation of the small bowel. Water soluble contrast media are contraindicated if there is any danger of aspiration into the lungs.

Sutton, D,1980 A textbook of Radiology & Imaging, Churchill Livingstone, London

I-X Barium Meal (ca. 1920s)
Barium sulfate is used as a contrast agent to improve the visualization of the gastrointestinal tract in an x-ray image.  In the early days (ca. 1910-1920), there were a few instances where barium sulfide, which is poisonous, was administered rather than barium sulfate. Not good. To prevent this from happening again, various companies marketed barium sulfate strictly for the x-ray market, often under their own brand names.
Size:  9" high and 9" in diameter
A major problem with barium sulfate is that is is not soluble in water. The best you can do is to keep it in a suspension. If it settles out during an x-ray exam, the images will be compromised. In addition, there is the possibility that the accumulated barium sulfate could block constrictions in the GI tract. In the 1920s, various formulas were developed to keep the barium in suspension, and one of the first to be marketed was I-X Barium Meal produced by Industrial X-ray Research Laboratories of St. Louis. So now you know what "I-X it stays up" means. Quoting a 1929 advertisement: "I-X Barium Meal really stays in suspension and actually eliminates constipation caused by taking Barium Sulphate internally."  This advertisement also announces "an improved package" that is different from the one pictured above. I assume the one shown here is the older design. For an informative historical discussion about the use of barium sulfate see "Roentgen and the New Light - Roentgen's Moment. Part 4: Of Gastrointestinal Radiology, Bread and Butter; or The Flowering of Barium Sulfate" by D. Patton. Invest. Radiology 29 (4): 472-479; 1994. References Industrial X-ray Research Laboratories advertisement. American Journal of Roentgenology and Radium Therapy. Volume 21.  1929. E.R. Grigg. Trail of the Invisible Light. Charles C Thomas, 1965.