Title: Dmitri Mendeleev
Content:  Dmitri Ivanovich Mendeleev (sometimes transliterated as Mendeleyev or Mendeleef) (Дмитрий Иванович Менделеев, tr. Dmitriy Ivanovich Mendeleyev ; 8 February 1834 – 2 February 1907 [ ) was a Russian chemist and inventor. He is best known for formulating the Periodic Law and creating a farsighted version of the periodic table of elements. He used the Periodic Law not only to correct the then-accepted properties of some known elements, such as the valence and atomic weight of uranium, but also to predict the properties of three elements that were yet to be discovered.
Title: Dmitri Mendeleev
Content:  propose a periodic table was Lothar Meyer, who published a paper in 1864 describing 28 elements classified by their valence, but with no predictions of new elements. After becoming a teacher in 1867, Mendeleev wrote Principles of Chemistry (Основы химии), which became the definitive textbook of its time. It was published in two volumes between 1868 and 1870, and Mendeleev wrote it as he was preparing a textbook for his course. This is when he made his most important discovery. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table; he claimed to have 
Title: Dmitri Mendeleev
Content:  the complete arrangement of the elements in a dream: "I saw in a dream a table where all elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper, only in one place did a correction later seem necessary." - Mendeleev, as quoted by Inostrantzev Unaware of the earlier work on periodic tables going on in the 1860s, he made the following table: By adding additional elements following this pattern, Mendeleev developed his extended version of the periodic table. On 6 March 1869, he made a formal presentation to the Russian Chemical Society, titled The Dependence between the Properties of the 
Title: 1869 in science
Content: March 6 – Dmitri Mendeleev makes a formal presentation of his periodic table to the Russian Chemical Society. ; June 15 – John Wesley Hyatt patents celluloid, in Albany, New York. ; July 15 – Hippolyte Mège-Mouriès files a patent for margarine (as oleomargarine) in France as a beef tallow and skimmed milk substitute for butter. ; German chemist Lothar Meyer makes a formal presentation of the revised and expanded version of his independently-created 1864 periodic table, „Die Natur der chemischen Elemente als Funktion ihrer Atomgewichte". ; Publication of Adolphe Wurtz's Dictionnaire de chimie pure et appliquée begins in Paris. 
Title: Timeline of United States discoveries
Content:  Nathaniel Kleitman with assistance from William C. Dement, a medical student at the time, in 1952 during their tenures at the University of Chicago. Kleitman and Aserinsky's seminal article was published September 10, 1953. Mendelevium is a synthetic element with the symbol Md (formerly Mv) and the atomic number 101. A metallic radioactive transuranic element of the actinides, mendelevium is usually synthesized by bombarding einsteinium with alpha particles and was named after the Russian chemist Dmitri Mendeleev, who was responsible for the Periodic Table. Mendelevium was co-discovered by Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson, and 
Title: Chemistry
Content:  elements in the 1860s by Dmitri Mendeleev and independently by several other scientists including Julius Lothar Meyer. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. At the turn of the twentieth century the theoretical underpinnings of chemistry were finally understood due to a series of remarkable discoveries that succeeded in probing and discovering the very nature of the internal structure of atoms. In 1897, J.J. Thomson of Cambridge University discovered the electron and soon after the French scientist Becquerel as well 
Title: Lothar Meyer
Content:  1869, Dmitri Mendeleev published a periodic table of all elements known at that time (he later predicted several new elements to complete the table, and corrected some atomic weights). A few months later, Meyer published a paper that included a revised version of his 1864 table that now included virtually all of the known elements, which was similar to the table published by Mendeleev: Meyer had developed his fuller periodic table independently, but he acknowledged Mendeleev's priority. Included in Meyer's paper was a line chart of atomic volumes as a function of atomic weights, showing graphically the periodicity of the elements. Like 
Title: 1860s
Content:  antiseptic in surgery, and publishing Antiseptic Principle of the Practice of Surgery. As a result, deaths from infections due to surgery greatly decrease. ; Gregor Mendel formulates Mendel's laws of inheritance, the basis for genetics, in a two-part paper written in 1865 and published in 1866, although it is largely ignored until 1900. ; Dmitri Mendeleev develops the modern periodic table ; Helium was first detected during the total solar eclipse of August 18, 1868, in parts of India. It was the first eclipse expedition in which a spectroscope was used. ; J. Norman Lockyer and Pierre Janssen are honored for their discovery of the nature of the Sun's prominences. They were the first to notice bright spectral emission lines when viewing the limb of the Sun without the aid of a total solar eclipse. ; 1862 International Exhibition in London, England and 1867 International Exposition in Paris. 
Title: History of chemistry
Content:   An important breakthrough in making sense of the list of known chemical elements (as well as in understanding the internal structure of atoms) was Dmitri Mendeleev's development of the first modern periodic table, or the periodic classification of the elements. Mendeleev, a Russian chemist, felt that there was some type of order to the elements and he spent more than thirteen years of his life collecting data and assembling the concept, initially with the idea of resolving some of the disorder in the field for his students. Mendeleev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or periodicity, of properties within groups 
Title: Mendeleev's predicted elements
Content:  Dmitri Mendeleev published a periodic table of the chemical elements in 1869 based on properties that appeared with some regularity as he laid out the elements from lightest to heaviest. When Mendeleev proposed his periodic table, he noted gaps in the table and predicted that then-unknown elements existed with properties appropriate to fill those gaps. He named them eka-boron, eka-aluminium, eka-silicon, and eka-manganese, with respective atomic masses of 44, 68, 72, and 100.

Question: what did dmitri mendeleev discover in 1869?
Answer: Periodic Table.