Colloidal Silver Iodide Compound and Preparation Method (Harry S. Kerlan, No. 1,907,498)
This patent, filed in 1927 and assigned to E. R. Squibb & Sons, describes a breakthrough in antiseptic chemistry: a reversible colloidal silver iodide compound. Unlike previous silver iodide preparations, Kerlan’s product retained its colloidal properties even after being dried into scales and possessed dramatically higher germicidal power, killing bacteria in under a minute.
1. The Chemical Innovation: Metathetical Reaction
Historically, colloidal silver iodide was made by treating metallic silver with iodine. Kerlan discovered that a metathetical reaction (an exchange of ions) produced a far more effective product.
The general chemical equation is:
AgX + MeI –> AgI + MeX
- AgX: A colloidal insoluble silver salt (such as silver chloride, oxide, or oxalate).
- MeI: An alkali metal iodide (like sodium iodide).
- AgI: The resulting yellow colloidal silver iodide.
- MeX: A soluble byproduct removed during purification.
2. The Preparation Process
The process is meticulously controlled to ensure the silver remains in a salt form rather than reducing to metallic silver, which Kerlan noted would “lose” the silver’s reactive potential.
- Protective Colloid: Gelatin is boiled with sodium hydroxide (hydrolyzed) to create a medium that prevents the silver particles from clumping together.
- Formation of the Precursor: Silver nitrate and sodium chloride are added to the gelatin to create colloidal silver chloride (a milky-white solution).
- Conversion: Sodium iodide is added slowly with mechanical agitation for three hours, converting the white chloride into yellow silver iodide.
- Purification (Dialysis): The mixture is dialyzed through membranes (like pig bladders) for 40 hours to remove impurities.
- Drying: The solution is evaporated in a vacuum to create yellowish scales.
3. Superior Germicidal Performance
The most significant claim of the patent is the speed of action. Kerlan provided extensive test data comparing his product (R-110) against the leading market products of the 1920s using Staphylococcus aureus.
| Product | Dilution | Result at 1 Minute | Result at 2 Minutes |
| Market Standard | 1-5 | Alive (X) | Alive (X) |
| Kerlan’s R-110 | 1-500 | Killed (-) | Killed (-) |
| Kerlan’s R-110 | 1-1000 | Killed (-) | Killed (-) |
Key Finding: Kerlan’s compound was found to be at least 60 times more powerful than existing silver iodides. He emphasized that the first minute of contact is the most important, as medical washes are often drained or washed away quickly by natural body fluids.
4. Medical Applications and Properties
The “reversible” nature of the colloid meant it could be shipped as dry scales and reconstituted by doctors or pharmacists without losing its potency.
- Non-Irritating: Unlike silver nitrate, which can sting or burn, a 10% solution of this colloidal silver iodide could be applied to the eyes multiple times a day for weeks with no irritation.
- Physical Traits: Odorless, tasteless, and stainless compared to other silver antiseptics.
- Usage: Specifically intended for the mucous membranes of the nose, throat, and eyes.
Technical Significance
Kerlan’s work for Squibb & Sons provided a highly stable, “instant-kill” antiseptic that was safe for sensitive tissues. While he admitted that chemical analysis couldn’t explain why this method worked better, he theorized it was due to a superior degree of dispersion (smaller, more evenly spread particles) or the specific shape of the silver iodide particles created during the ion exchange.
